Only some schools in Wales will benefit from a budget bounty of up to pound;13 million next year - unlike in England, where every primary and secondary will get a cash bonus from last week's budget statement.
The Assembly government says the pound;13 million is "at least equivalent"
to Chancellor Gordon Brown's handout to schools in England.
But a spokesperson confirmed this week that only some Welsh headteachers will receive extra money, as the cash will be focused on the most disadvantaged pupils.
Heads and some classroom unions are angry, saying money should be passported directly to all schools. But the National Union of Teachers Cymru said cash should be focused on those schools most in need of extra support - although it is opposed to any system of bidding for the money.
Brian Rowlands, secretary of the Association of School and College Leaders Cymru, said: "This money should be passported by local authorities directly to schools, as it is in England. Heads in Wales become increasingly frustrated when they see colleagues in England receiving large amounts sent directly to them over the past three years, and guaranteed for the next three. This allows for sensible planning and removes worry each year."
But he welcomed the extra money for public services announced by the Chancellor - pound;45m over two years in Wales - adding: "We trust that the Assembly government will ensure that education receives its correct share.
"This is sorely needed in the light of the dire budget settlements in Wales for 2006-7, which will leave many schools in deficit."
Gethin Lewis, secretary of NUT Cymru, said it was opposed to any system requiring LEAs or schools to bid for a share of the pound;13m because of the additional bureaucracy involved.
But money should be focused on those most in need, and he suggested schools with large budget surpluses should not be priorities.
"We want the money to go to the schools where it make a difference, prevents compulsory redundancies and improves the achievements of pupils,"
An Assembly government spokesperson said further announcements on how the pound;13m will be used will be made next week.
She added: "We can say that it will be distributed via the specific grant mechanism, will focus on the disadvantaged, and will not therefore be going to all schools."
First Minister Rhodri Morgan said this week his priority was to improve the life chances of Wales's "substantial wedge of children" who leave school with no qualifications. Mr Morgan said he wanted to boost "outcomes from the education system" of children who do badly in school.
"They are not special needs, they are not academic. They are somewhere in the middle," he said.
English schools will receive pound;220m next year and pound;565m in 2007-8. Wales has pound;17m extra to spend on public services in 20067, with the pound;4m not allocated to education going on drugs, alcohol, domestic abuse and anti-social behaviour schemes. It is not yet known how the pound;28m pledged for 20078 will be allocated.