Cold tea, endless emails and no time to pee - this is the average day for a Kiwi teacher.

"I chose to be a teacher. I didn't choose to be undervalued by the Ministry of Education."

West Auckland teacher Charlee Jobson is one of many who will be striking on August 15.

Fed up with the "real misconceptions" about what teachers do, she wrote a widely shared letter on Facebook about what teaching really looks like, and why she'll be downing tools on Wednesday.

Teaching isn't the 9am to 3pm job some people seem to think it is, she says - it's early morning meetings, late nights planning, going to work ill, and not even having time for a bathroom break.

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Primary teachers are currently entitled to 10 hours' classroom release time each term. That's time for things such as planning, reporting and research.

The Government's latest offer to teachers increases this to 12 hours - or an additional 12 minutes a week.

"We teach during the school day. We plan on our own time.

"After a long day of meetings, duties, and teaching, the laptop comes out and the paperwork begins."

It's not just planning and marking, either: it's rehearsals, performances, galas, parents' evenings, meetings and professional development, in break times, evenings, weekends - and holidays.

Teachers' holidays are a particular bugbear for people criticising the strike.

But Jobson says you can't blame teachers for the structure of the school year.

"Walk into a classroom in week 9 or 10 of a school term and you'll see the state the children are in by that stage. We have to have those holidays for kids, we don't get to choose that as teachers," she says.

"Holidays are awesome, they're a great perk, but they're a reality of the job."

Jobson also takes issue with the idea teachers should put up with bad pay and long hours because it's the "status quo".

"Even though I understood it coming in, it doesn't mean I shouldn't push for improvement.

"I should ask for more, and I should be teaching my students to value themselves and ask for more."

Supplied Teaching is far more than a 9am to 3pm job, says primary teacher Charlee Jobson.

Her students may only be in Year 5, but they're getting the message.

Jobson says she outlined the strike to her class, then told them to do their own research and talk to their parents about it.

"A lot of them have come back saying they value me and they respect me and they want me to feel valued and respected.

"You don't often get that feeling back from students."

People need to remember the strike is as much for the kids as it is their teachers, Jobson says - "which always sounds funny when it's adults asking for more money".

The nationwide teacher shortage means schools often struggle to find relievers when teachers are ill.

If a relief teacher can't be found, classes will often be split, with a few children sent to each of the surrounding classes armed with a pile of books and worksheets for the day.

"There goes any semblance of individualised learning," Jobson says.

The guilt of doing this means she'll often come into school when she's ill.

"When I wake up and I'm feeling like absolute hell, I just think of my class and the sad faces they give me when they say they're going to be split […] I drag myself out of bed and go in.

"Teachers are quite selfless in nature, but I don't think we should be quite at that point of desperation."

Teachers' union, the New Zealand Educational Institute (NZEI), recently said the teacher shortage was moving "from a crisis to a disaster".

It predicts by 2030, New Zealand may be missing as many as 2000 primary teachers.

At the coalface of teaching, it's "pretty dire", Jobson says.

Striking wasn't a decision taken lightly by teachers, and Jobson says she understands schools closing for the day may put a financial strain on parents.

"I know there are parents who are really at their limits - as soon as a child is sick it's really tough to take a day off.

"Essentially this is about the wellbeing of children ... We're no longer going to be able to staff our classrooms unless we have a big change like this.

"If they can get on board and support us then it's going to benefit their kids in the long run."

Education Minister Chris Hipkins has previously said he'd prefer the strike was cancelled in favour of further bargaining and discussion on the issue.

Speaking earlier this week, he said the Government's current offer was already double, on average, what the primary school sector received under the National Government.

The Ministry of Education has offered pay rises over three years, ranging from 6.1 per cent at the top of the pay scale – making the maximum salary about $80,600 – to a 14.7 per cent rise on the entry salary of $47,980 for university trained teachers, bringing it to $55,030.

Read the full text of Charlee Jobson's open letter: