THREE Scottish primary heads are taking their local authority to industrial tribunal to win equal pay with their secondary-school peers. The heads, all women, earn around pound;7,000 less than the heads of their local South Ayrshire secondaries, despite having the same numbers of pupils. They say the gap breaches the Equal Pay Act 1970 and amounts to sex discrimination, since most primary heads are women and most secondary heads are men. South Ayrshire Council is fighting the action, saying there are substantial differences in duties.