Truancy has become an alarming problem. No one knows how many children ' bunk off' school. Some experts put the figure as high as half a million a day. The teacher shortage, raising the school leaving age, overcrowded classrooms, difficult family backgrounds, all contribute to the problem. In the London borough of Tower Hamlets - where more than 600 schoolchildren are absent every day-two teachers have set up an experimental school for truants aged 8-15 in a crypt under a church. Experts who realise that the juvenile court is not an answer to the problem are watching with interest as this tiny experimental school grows. Already there is a 100% regular attendance; now the children are pleading for the school to stay open at weekends.