P214 CEEFAX 214 Tue 15 May 21:24/59       Members of the teachers' union MAS/UWT have staged half-day strikes in about 25 secondary schools in Cambridgeshire. Many pupils weti sent home for all or part of the day, but examination classes were not affected. A union spokesman said action will continue in the county during the week. The county's third largest teaching union, the Assistant Masters and Mistresses Association, has voted not to provide covet for colleagues from othjt unions taking industrial action eithjt today or in future. News index 102/202 Newsreel 119/219