The force of the explosion that destroyed Shifa Salman's house in the northern Gaza district of Jabal al-Rayas folded floor into floor as easily as pastry. It pushed pillars through concrete, reconfiguring her home into a bristling dome. The tail-fin of one of the Israeli bombs responsible still sits on top of the rubble, innocuous as a child's discarded toy. These days, pigeons and sparrows nest in the cave-like space carved out by the detonation inside the ruins where mattresses and bags of flour are stored, the latter stencilled with the initials of the World Food Programme. Sleek, aggressive cockerels patrol the floor, flying at intruders.

Six months after Israel's war against Gaza, Shifa, a 20-year-old student, sleeps with her family behind the fallen house. A trodden path leads through the rubble to a row of cramped, ramshackle shelters open to the elements and roofed with hessian sacks. They are identical to the cattle pens that stand beside them.

On closer examination I can see that the frames have been constructed out of cast-off sections of wood and metal lashed together. What walls that exist are fashioned out of old pallets and branches woven into crude wicker. Or more sacking, staked into the soil to make rudimentary windbreaks.

Shifa's family are Bedouin. Until recently they farmed this land close to the barrier, in an area once used for missile launches against the Jewish communities on the far side. This was one of Gaza's limited areas of agricultural production in a densely crowded urban area, home to 1.4 million people. Because of the missiles, this neighbourhood of farms and little factories was treated to a scorched earth policy.

Inside Shifa's own tiny, dirt-floored "compound" a fire pit has been scooped out of the earth and filled with twigs. On it sits the blackened pan in which Shifa and her mother make stews of molokhiya - spinach-like greens - with chicken, garlic and onions. "This is my kitchen," says Shifa shyly, in English. A piece of broken board is propped on two drums to function as table. Here a jam jar sits, holding a pestle and a solitary sharp knife.

I first came to this house in January, in the immediate aftermath of Israel's war against Gaza, visiting the Salman family almost every day. The family were sleeping in the ruins to shelter from the rain, surrounded by the stinking bodies of their sheep, killed during the assault. Then, Shifa complained that the frightened younger children were kept awake at night by the sound of packs of dogs scavenging among the carrion outside.

A slight and pretty woman with dark brows, Shifa is walking along a road where the ruined houses of her neighbourhood stand on each side like stone-piled graves in a desert. It is 7am and she is on her way to meet the bus that will take her to university. She is wearing a black abaya, the head-to-ankle veil that is the uniform of the university, and carrying a pile of her books. Both books and the veil were donated by the college after Shifa's family lost most of what it owned. "There used to be a factory here," says Shifa, pointing at a collapsed, blue-painted metal structure. I am reminded of the last time I saw this building. A herd of cows lay slaughtered in the field outside.

"My life used to be so good when we had a home. Now it is awful." She wipes a tear away, trying to hide what she is doing. "This street used to be full of cars," Shifa explains. "It was easy to get to university. Now I have to walk for half an hour before I can get a ride. There used to be houses here, but everyone fled after the F-16s attacked. After the tanks attacked. Only a few of us have stayed."

So few, in fact, I quickly learn their names. There is the Khader family, who have built a complex cloth-walled shelter on top of the ruins of one of their houses, a structure that has expanded over the months as new rooms have been added. One day I find the men of the family crawling into a dark hole beneath the house to chip out tiles from what was once their ground floor to sell for food, disturbing a nest of pinkly squirming newborn mice.

There is the owner of the dairy parlour, Mohammed al-Fayoun, whose cattle were killed. He has set up business again beneath the bent and twisted rafters of his metal roof, where he sits daily in a plastic chair. He complains his customers are still too scared to visit him this close to the border with Israel.

While her fathers and uncles work the land, Shifa is representative of a new generation - the first from her family to go to university. She says she wants to be a geography teacher and has an exam today. "I used to have a television in my room," she says, passing the house of Nabil Nasser Hassan, once one of her neighbours, whose demolished home is now surrounded by a stockade of corrugated metal sheeting to keep out looters hunting for pipes and wire to recycle. "At the beginning, people came to give us coupons and blankets. But no one has come to see us for a long time. No one has spoken to us about rebuilding our home. I'm scared living where we live. All of the family is, especially my sister Safa when she hears the [Israeli] jets."

It is not only Shifa's daily walk at 7am through the ruins to reach the Islamic University that is a mark of her changed life. Before the destruction visited by the bombs, tanks and bulldozers, Shifa says, she would sit up after dark, reading her books in her own room, which was decorated with posters of animals. Now when the light fades, she must cease her studying. "I used to spend all night working. I'm good," she says with confidence. "But now I'm struggling. And I know if I can succeed, I can make life better for my family."

Israel's Operation Cast Lead began on 27 December 2008. By the time of its conclusion on 18 January, with the declaration by both Israel and Hamas - which governs Gaza - of their own unilateral ceasefires, more than 1,300 Palestinians had been killed, many of them civilians. They had perished under an Israeli rain of bombs, bullets, missiles and artillery fire, including white phosphorous munitions.

While Israel insisted the war was designed to bring a halt to the launching of home-made missiles out of the Gaza Strip, its targets suggested wider aims, not least the dismantling of Palestinian institutions. Police stations, ministries, schools and hospitals were hit. Orange groves and tunnel tents for growing strawberries and vegetables were uprooted. And thousands of houses were damaged.

On my return, I scour Gaza for evidence that anything has changed for the better in the months since the war ended. But houses and other buildings destroyed during the conflict remain as hollowed-out and dusty monuments to violence. In places, some owners have experimented with repairing buildings with an adobe made of mud and straw baked in the sun. But it is a very temporary solution.

In the office of Dr Ibrahim Radwan, the man appointed by the Hamas government to record the damage done in Israel's three-week war, I jot down the numbers that describe what happened. Some 3,800 homes and businesses badly damaged in one way or another - although he admits this includes some damaged in previous Israeli attacks. In addition, 80 government buildings were hit. Radwan has his own categories to describe the degrees of destruction, but after a week driving around Gaza, the damage conforms to its own types. The big metal walls of the workshops on Salahadeen Road, where the heaviest fighting took place, now leak light through hundreds of bullet perforations; other walls are splashed with the shrapnel of missiles fired from drones; blocks of flats hit by artillery fire show scorched holes. And across the north of the Gaza Strip stand the weird igloos of the bomb-flattened houses.

There are changes that I do register in the six months since the war ended. The bodies of dead animals have been removed and cleared away; the ruins have been sifted for human remains. It has expunged the odour of decay that was once tangy with the chemical flavour of explosives and spent phosphorous. The tangled remnants of an orange grove I drove past every day, tipped over and torn by military bull-dozers, has disappeared, razed for firewood.

And without concrete and steel, aluminium and glass, without tiles for roofs and cladding for stairs and bathrooms - all prevented from entering Gaza by Israel's continuing economic blockade - no rebuilding has begun. For those who suffered most, the war continues.

I run into Shifa's father by chance one day at Gaza City's flea market, in the Yarmouk district. He tells me he comes once every fortnight to look through stalls selling broken and unwanted things in the hope of finding something that might alleviate their circumstances. He shows me the contents of his white plastic shopping bag: two plastic joints for connecting water pipes. Bought in the hope that he might one day have a use for them.

It is not only the physical symptoms that persist as a reminder of what happened in Gaza. Sana al-Ar's family live in a light but sparsely furnished fifth-floor flat in a tower block in Shujaiya. There are photographs on the wall of 16-year-old Sana's younger brothers, Rakan and Ibrahim, and her father Mohammed - all killed during Israel's attack. Missing are pictures of her 18-year-old sister, Fida, and her brother's wife, Iman, who also perished. In a room decorated with gold curtains and floor cushions, Malak, the youngest surviving child, plays on the carpet, in a T-shirt printed with the slogan "Daddy's Little Tiger". But Daddy is gone.

On 3 January, Israeli tanks attacked the area where Sana and her family lived. Their house - like Shifa's - was located close to the border, not far from a pretty, gold-domed mosque and a graveyard. Shifa Salman's family managed to flee. But Sana's family - her mother says - were blown to "pieces of meat". It is left to Sana's grandmother to recount the story, while the girl and her mother listen. She tells how a rocket hit the house, injuring Fida with shrapnel. She quickly bled to death. The father told the family to flee in their donkey cart, but a second missile exploded, fatally injuring him, too. I listen as Sana's grandmother describes how in the smoke from the explosion the weeping mother found her son Ibrahim "missing half his face". The family gathered what they could of their dead in a blanket and took them to a neighbour's house, where they were trapped, sitting with the bodies, for five days.

I had heard about Sana in January, from Dr Fadel Abu Hein at Gaza City's Community Training Centre and Crisis Management. Fadel was sending teams of social workers and therapists to run workshops for the most badly affected children, even working with them as they sat on blankets in the rubble. As we talked about the types of trauma suffered by children during the conflict, he mentioned a girl who had seen most of her family die and had spent days trapped with their bodies. I had met her the following day, at the house of an uncle she was staying with. And I had tried to talk to Sana then. But sitting on a bed in a cold, bare basement room, she had been withdrawn behind a wall of grief, managing to speak barely a handful of words. Instead, it was the other relatives who had crowded the room who supplied answers to my questions. The only thing I learned was that she liked to paint, and so I had bought her pens and paper, since all of hers were lost.

Sitting in her new flat, Sana fetches the only drawing she says she has done since the killing of her brothers - in charcoal grey, against a shaded blue background, are the names of the boys. A day later, I learn from Nahid Hanrarah, the social worker who has worked most closely with Sana, that she has done other paintings, paintings of her family drenched in blood.

"Painting their names is an improvement," Nahid says. He adds that Sana is much improved, but when I ask her questions, she answers in fragmented sentences: "Things aren't too much better. Everything is still... I feel things are separate. The anger and the sadness. The one who could make us happy [Sana's father] is the one we've lost."

There are long pauses when Sana looks away. "People have tried to help me. There have been people at school ... " Sana mentions her irritation at those among her friends who insist on trying to talk to her about what happened on 3 January and in the days that followed. "I feel I can't concentrate at school like I used to," Sana explains. "I hate it because people at school keep asking how my family died. They think if I talk then it will help me. That is why I went to see Nahid. Because it makes me so upset.

I don't want to talk about it." Sana is also scared to go to the bathroom alone and, she tells me, she suffers with nightmares. I learn from talking to Nahid that Sana was suicidal when she was first referred to him. "She didn't want to live. She had no hope," he explains quietly.

It has not only been at school where Sana has been confronted by what happened. At home, too, she has had to deal with constant reminders of her loss from her mother, Laila, whose grief is even more debilitating.

"I think," Nahid suggests, "that Sana is the only one in the immediate family who really understands what happened to them, and who can help the family. Her mother can't do anything, really. So the responsibility has fallen on Sana. Sana is growing [as a person] from the knowledge of all the things that she passed through, which is helping her to overcome. But it is a process that is far from complete. They were a family of nine, now only four are left."

There are moments when you see an echo of how this family must once have been. Before the Israeli soldiers came. Before the war. Malak crawls on to her mother's knee with her doll and squeals loudly: "Bite her! Bite her!" Suddenly I realise that Sana is smiling at her mother. It is the first time in five visits to this family that I have seen her smile. And when she does, another girl is briefly visible.

And Sana is smiling again when I next see her. We are talking about ordinary things other than the horror that befell her; about the films she likes to watch - Bollywood and action films, X-Men - about her new computer, and the internet connection she is waiting for with excitement: "Before, we didn't have a computer. I've had it two weeks." Then the pain is in the room again. "The first thing I'm going to do is put pictures on it of my father and my sister and my brothers." She seems sad, but not unreachable. I ask Sana if she will be going to the beach in the holidays, but it is her mother who answers: "We used to go to the sea, all of us together. We don't go any more ... " There are ghosts in the room that Laila cannot ignore. And because Laila cannot ignore them, Sana is also bound to observe them, and to mirror her mother's grief.

Laila says she has nothing left, and I remind her of Sana and Malak. She looks up at the pictures above her. "Rakan was the most beautiful," she sobs, as Sana begins to cry, quietly. "He was only four and a half. He was a very naughty boy. People kept saying to his father: 'This boy will be someone.'" When his sister went to carry him, I did not recognise him. He had come to pieces."

In Dr Fadel's office, decorated with pictures of dead Palestinian fighters, he tries to assess what has changed and what has not. Some people have begun to rebuild their lives, while others living in tents, or displaced, or living - like Shifa's family - among the ruins remain largely in the circumstances they were in when the war ended. "The biggest obstacle that we are facing is among those people whose problems have not ended - who live in a continuing war atmosphere. Nothing is happening about the destroyed homes, because we live in a continuing state of economic siege. So there are people still living in tents, or in the rubble."

Visiting his office one day I am confronted with evidence of how those dealing with damage from the conflict can progress. Hanging on one wall are pictures drawn by trauma-affected children, before-and-after images whose real subject is the effects of exposure to violence, and how it can be mediated. The "before" pictures show soldiers with guns, tanks and jets, images of destruction and death. The "after" pictures show the ordinary stuff of childhood: flying kites and images of family and friends and flowers, produced after lengthy work with the centre's social workers. I mistakenly believe that they come from the recent conflict. I am informed that they pre-date the war - describing the experience of Israeli military incursions and air strikes. When I ask to see drawings produced after the January war I am led to another series of sketches that depict - so far - only fighting. And examining them, I am reminded of another picture I had seen a few days before in Khan Younis, in Gaza's south, in a child's bedroom.

I had first encountered Rewa'a Omer, aged 30, in the Nasser Hospital, standing between the beds of her two children, her daughter Ola and her son Yahya. It was a few days after the ceasefire and Rewa'a was clutching a bloody piece of clothing. An hour or so before, 10-year-old Ola, and Yahya, nine, had been standing close to their school gates with a group of other primary school children, waiting for a lift to take them home. As they stood chatting, an Israeli drone had fired a missile at a passing Hamas fighter on a motorbike three metres from the children. The blast had driven shrapnel into the legs of the children and a sliver into Yahya's eye.

Until I see the poster in Ola's bedroom, I think she has recovered better than her brother. It depicts a baby's smiling face. But someone has drawn trickles of blood coming from the nose and mouth, and added small scarlet cuts. Rewa'a tells me it was Ola who had disfigured it. I notice, too, that she has shaded around the baby's eyes so that the skin appears yellow. I think of how her brother's face was in his hospital bed, bruised under the bandages and stained with something like iodine.

Rewa'a's family are what passes for middle class in Gaza. Her husband was a police captain in the Palestinian National Authority before Hamas's assumption of full executive power in 2007, at the end of the most violent period of the so-called "internal fighting" between Fatah and Hamas. He does not work now but still receives his salary. Well-educated, Rewa'a speaks excellent English. The family asks me for a copy of the photograph I took on the day the children were injured, and Rewa'a shows me an image saved on her phone, given to her by a neighbour, that shows her son being carried from the scene in someone's arms, his head limp and bloody. "It was on the television. And I was not there to protect them." There are still some marks on her daughter's legs, like dark bruises. "My son was injured worse," she says. "He is still shy about wearing shorts because of the scarring. There was shrapnel in his eye that we did not know about. He had to go to Egypt to be operated on. They have recovered physically," Rewa'a adds, "but emotionally my daughter is more damaged than my son. That first time that she saw her brother bleeding has stuck with her. I think it will always be inside. She talks about what happened and her grades at school have suffered. It was a month and a half before she was ready to go back to school."

Rewa'a says that Ola is still frightened to go to the bus stop, and "the children are always fighting now. I worry all the time about them, waiting for them to come home from school."

Ola wants to tell the story of what happened to her. "The car was late. There was a sound and I woke up and everything was black. Things were broken and bleeding. Then people came to rescue my brother. Someone took my hand. I said: 'My brother! My brother!'" I ask Ola what she would like most. She does not have to think about it: "I would like to live somewhere safe."

Yahya wants to talk about Egypt, where he went to have the shrapnel taken from his eye.

"I went to the zoo and saw the pyramids!"

"I feel that there is nowhere safe in Gaza any more," adds Rewa'a. "I used to think before that ... you know, we are ordinary people. This [the violence] had nothing to do with me."

When I visit Rewa'a again we climb up on to the flat roof of their building. Fading home-made kites are propped in tangles of string against the balustrade. Rewa'a seems oppressed by the thought of what has happened. "I wish that they could have a normal childhood. I didn't grow up in Gaza, I grew up in Saudi Arabia. I came back to Gaza when I was 16. I had a beautiful childhood. I want the same for them. Not this.

"Every time the summer holidays come round I wish there was something that they could do. Hobbies that could help them grow. But there is nothing here like that." I remind her of something that Yahya told me when I asked what he wanted to be when he grew up. He replied that he wanted to be a fighter. "Yahya says that. But it is just an idea in his head."

As we are leaving I ask Rewa'a if she has any hope that things might change in Gaza. She seems sad. "Nothing ever changes. There is no rebuilding. Everything becomes worse.

Nothing here ever changes for the better."

• The Secret Life of War: Journeys Through Modern Conflict by Peter Beaumont is published by Harvill Secker.