Jenny is very tall for her age, and when her mum makes her dress smartly for her first day at a new school, she looks very grown-up indeed. So grown-up, in fact, that when she arrives at the school, she is mistaken for a new teacher, and left in charge of a classroom of kids! Jenny's first instinct is to escape, but on her way out she gets caught by Miss Ice, the strict school principal, who is not very impressed to find a new teacher sneaking around the corridors. Petrified by the terrifying Miss Ice, Jenny is forced to keep up the act, and soon finds herself in all sorts of tricky situations, culminating in a rather explosive chemistry lesson. How long will it be before Jenny is found out? Will she and her pupils survive the day? Whatever happens, it's going to be a real education!