Teaching assistant numbers have increased by an average of 660 a year since 1998, alongside a smaller but steady increase in administrative staff. More and better-qualified teaching assistants are expected to provide much of the cover that will be needed from September 2005, when all teachers will be entitled to 10 per cent non-contact time under the terms of the workforce agreement signed in January 2003.
Statistics released by the Welsh Assembly government claim the number of support staff in schools increased by around 400 between January 2003-4.
But this is almost entirely accounted for by a 422 rise in the number of nursing and childcare staff in schools.
The number of teaching assistants, including for special needs, is down 61 - compensated for by an identical increase in administrative staff. The number of technicians is also down slightly.
Anna Brychan, director of NAHTCymru, said: "We are concerned about this because it suggests the workload money is not having the intended effect.
With non-contact time coming up, that's a serious worry."
Geraint Davies, secretary of the National Association of Schoolmasters Union of Women Teachers Cymru, blamed falling pupil numbers and school budget cut-backs for the reduction in teaching assistants. He said schools should be taking on more support staff, not fewer, in preparation for next year's non-contact-time needs.
"In trying to balance their budgets, too many schools in Wales terminated the contracts of support staff. That has been disappointing "We should see an increase in new staff being employed, properly trained and paid."
However, the National Union of Teachers Cymru is still arguing that qualified teachers should be used to cover non-contact time - not assistants. Heledd Hayes, the union's education officer, said: "We would want teachers to be covered by qualified teachers. We have had a positive response from parents and governors to this."
* The same report reveals nearly 60 per cent of pupils in schools in Wales consider themselves to be Welsh - with nearly a quarter describing themselves as British and less than 6 per cent as English. Asian, Black, Chinese and other ethnic-minority children in Wales are more likely to describe themselves as British, but most mixed-race youngsters consider themselves Welsh. Half of Black children are eligible for free school meals, compared to only 17.7 per cent of white classmates.