Jean Kennedy has degrees in biology and a Master’s in special education. Now, she’s trying to decide what to do with her third degree: a certificate of achievement from Oaksterdam University, the Harvard Business School of marijuana.

“I’m Italian,” said Ms Kennedy, 56, a retired high school biology teacher with graying hair and a heavy New York accent. “You know Italians, we grow tomatoes. Maybe I’ll grow some plants.”

Horticulture 102 is one of the many subjects she studies at Oaksterdam, whose campus is set amid the hip cafés, restaurants and cannabis dispensaries of downtown Oakland. Founded in 2007, the school sees itself as a training ground for citizen advocates in the fight to legalise marijuana.

Oaksterdam is rebounding after a 2012 raid by the federal government, which deems marijuana a Schedule One illegal drug – the same category as cocaine and heroin. Federal agents, many of them masked and armed, broke down the doors with battering rams, carting away an estimated 60,000 cannabis plants and scattering the school’s terrified faculty and students.

Where cannabis is and isn't legal Show all 10 1 /10 Where cannabis is and isn't legal Where cannabis is and isn't legal UK Having been reclassified in 2009 from a Class C to a Class B drug, cannabis is now the most used illegal drug within the United Kingdom. The UK is also, however, the only country where Sativex – a prescribed drug that helps to combat muscle spasms in multiple sclerosis and contains some ingredients that are also found in cannabis - is licensed as a treatment Getty Where cannabis is and isn't legal North Korea Although many people believe the consumption of cannabis in North Korea to be legal, the official law regarding the drug has never been made entirely clear whilst under Kim Jong Un’s regime. However, it is said that the North Korean leader himself has openly said that he does not consider cannabis to be a drug and his regime doesn’t take any issue with the consumption or sale of the drug MARCEL VAN HOORN/AFP/Getty Images Where cannabis is and isn't legal Netherlands In the Netherlands smoking cannabis is legal, given that it is smoked within the designated ‘smoking areas’ and you don’t possess more than 5 grams for personal use. It is also legal to sell the substance, but only in specified coffee shops Getty Where cannabis is and isn't legal USA Although in some states of America cannabis has now been legalised, prior to the legalisation, police in the U.S. could make a marijuana-related arrest every 42 seconds, according to US News and World Report. The country also used to spend around $3.6 billion a year enforcing marijuana law, the American Civil Liberties Union notes AP Photo/Ted S. Warren Where cannabis is and isn't legal Spain Despite cannabis being officially illegal in Spain, the European hotspot has recently started to be branded, ‘the new Amsterdam’. This is because across Spain there are over 700 ‘Cannabis Clubs’ – these are considered legal venues to consume cannabis in because the consumption of the drug is in private, and not in public. These figures have risen dramatically in the last three years – in 2010 there were just 40 Cannabis Clubs in the whole of Spain. Recent figures also show that in Catalonia alone there are 165,000 registered members of cannabis clubs – this amounts to over 5 million euros (£4 million) in revenue each month Getty Where cannabis is and isn't legal Uruguay In December 2013, the House of Representatives and Senate passed a bill legalizing and regulating the production and sale of the drug. But the president has since postponed the legalization of cannabis until to 2015 and when it is made legal, it will be the authorities who will grow the cannabis that can be sold legally. Buyers must be 18 or older, residents of Uruguay, and must register with the authorities Getty Where cannabis is and isn't legal Pakistan Despite the fact that laws prohibiting the sale and misuse of cannabis exist and is considered a habit only entertained by lower-income groups, it is very rarely enforced. The occasional use of cannabis in community gatherings is broadly tolerated as a centuries old custom. The open use of cannabis by Sufis and Hindus as a means to induce euphoria has never been challenged by the state. Further, large tracts of cannabis grow unchecked in the wild Getty Where cannabis is and isn't legal Portugal In 2001, Portugal became the first country in the world to decriminalize the use of all drugs, and started treating drug users as sick people, instead of criminals. However, you can still be arrested or assigned mandatory rehab if you are caught several times in possession of drugs Getty Where cannabis is and isn't legal Puerto Rico Although the use of cannabis is currently illegal, it is said that Puerto Rico are in the process of decriminalising it RAUL ARBOLEDA/AFP/Getty Images Where cannabis is and isn't legal China Cannabis is grown in the wild and has been used to treat conditions such as gout and malaria. But, officially the substance is illegal to consume, possess and sell Getty

The university was devastated by the raid, which Oaksterdam founder Richard Lee dismissed as a “last-ditch effort” by federal authorities to enforce marijuana laws that are out of step with the times.

Medical marijuana was approved by Californian voters in 1996. In the years since the raid, four states and the District of Columbia have legalised pot, making it a legitimate business in parts of America, worth an estimated $3.5bn (£2.3bn) a year.

Still, as Oaksterdam preaches the gospel of pot entrepreneurism, its history offers a lesson in harsh reality. Robert Raich, a lawyer who has twice argued legalisation cases before the US Supreme Court, makes that lesson explicit in “Cannabusiness 102”, where he warns students of the risk inherent in cultivating the drug. “Until the federal government changes the Controlled Substances Act,” Mr Raich said, “I teach how to create defences against possible hostile action.”

Business at Oaksterdam is booming despite that risk. The school employs 20 staff members and 150 instructors, including some of the biggest stars in the cannabis universe. Debby Goldsberry co-founded the Berkeley Patients Group medical cannabis collective, and Ed Rosenthal is often cited as the world’s leading authority on marijuana cultivation. The Oakland lecture hall holds 50 students and every seat is paid for.

There is a new campus in the works in Las Vegas, where two four-day seminars sold out this year, with 250 students paying as much as $995 apiece. Last month, the school conducted a conference in Orlando, where about 300 doctors and nurses earned continuing education credits after learning to use cannabis to treat an array of medical conditions, including glaucoma and glioblastoma.

And the school routinely advises politicians from places including California and Jamaica on topics such as how to appraise applications for medical marijuana and dispensary licences, and how to promote marijuana research.

At the main campus, the walls display photos of the school’s 23,000 graduates, who range in age from 18 to 65 and represent every state and 30 countries. Last month, 30 Californian lawmakers drove from Sacramento for lectures on taxation and regulation, studying for the possible passage next autumn of an initiative that would legalise marijuana for recreational use.

Aseem Sappal, the school’s provost and dean, said he wants to build Oaksterdam’s credibility as a serious institution of higher learning. “We have scepticism because it’s a big joke, people just smoking pot. But the country is moving in this direction for a reason,” Mr Sappal said.

As the legalisation movement grows, Oaksterdam is attracting students who say they have never smoked pot. One is Ms Kennedy, whose primary interest is in the plant’s medicinal benefits. “These are not crazy people. These are not potheads,” she said. “When you come here, you see it: these are businesspeople.”