If you are a newly-qualified teacher starting your first year in the classroom, prepare for bad news: your happiness levels could plummet until Christmas.
The mood change is revealed in a graph which plots the months of the school year against a "positiveness" scale from zero to 120 points.
The graph features in Helping Teachers Develop, a new book by Sara Bubb, The TES agony aunt for new teachers and an academic at London university's institute of education.
She estimates that NQTs start with a positiveness score of 80 which sinks from September to November, then plunges to zero in the run-up to Christmas.
"They start on a high in September, but then reality strikes and they live from day to day, needing quick fixes and tips for survival," she writes.
"Behaviour management is of particular concern but they're too stressed and busy to reflect. Colds and sore throats seem permanent."
Luckily, happiness levels appear to rise from January onwards, reaching the 60 mark around Easter and soaring past 100 by the end of the summer term.
"In January, pupils return calmer and ready to work," Ms Bubb writes.
"Teachers can identify difficulties and think of solutions. They feel they are mastering teaching and begin to enjoy it."
The graph was inspired by a similar one produced for American teachers by Ellen Moir of California university, which Ms Bubb adjusted using UK term-times and evidence from British teachers.
Ms Bubb said that a similar pattern for the year applied for experienced teachers as well.
"Teachers always seem relieved when I show them the graph because they realise they are not the only ones who have felt like that," she said.
The book explores ways teachers at all levels can mentor others and improve their careers, by seeing through the jargon in job advertisements, for example (see box).
It makes extensive use of teachers' suggestions and complaints from The TES online staffroom. (www.tes.co.ukstaffroom) Several newly-qualified teachers who are quoted describe the poor support they have received from their induction tutors.
"Mine is never there," one said. "He has a mug with 'I'm so effing cool' on it and a picture of a guy in a hammock smoking a spliff. He calls the kids half-wits."
The book also contains guidance on ways to cope with having your lessons observed and how to make constructive comments as an observer. Examples of poor lesson observation include cases where the observer arrived late, looked bored and even fell asleep.
Helping Teachers Develop is published on September 9 by Paul Chapman Publishing, pound;15.99