Thousands of children are being taught in prefabs and school halls as the Ministry of Education struggles to get new classrooms built by an overstretched building industry.

Figures buried in the May 30 Budget documents reveal the ministry has underspent its capital budget by a record $176 million in the year to June 30 because of "capacity constraints within the construction industry".

In Auckland, 45 per cent (361) of the 805 new classrooms added to state schools in the four years to last June were temporary teaching spaces (prefabs).

Two temporary classrooms installed several years ago at Te Kura Kaupapa