Free material provided by banks that are being used to give lessons on financial literacy are often "tainted" by "covert advertising", a group of Assembly Members has heard.
A report from the cross-party Communities and Culture Committee has called for financial education to become a compulsory part of PSE lessons.
Teaching union ATL Cymru claimed that in some schools it amounts to little more than downloading material from the websites of major financial institutions, which is then adapted to fill the PSE slot.
"Clear guidelines are needed and adequately resourced training for teachers," said a union spokesman.
"`Pure' resources that are not tainted by financial institutions' overt or covert advertising are necessary."
The committee said it was "concerned" by the claim and called for a "central hub" of information including a directory of approved resources for financial education.
The committee heard that although financial education has been prioritised by the Welsh Assembly government, its delivery is inconsistent and many schools devote limited time to the subject.
There was also concern that in some schools the subject is "watered down" because teachers do not understand finance and lack the confidence to teach money issues.
Some schools provide good financial education by collaborating with credit unions and Citizens Advice, and some give pupils the chance to study financial qualifications from the ifs School of Finance, equivalent to GCSEs, AS and A-levels.
However, there are fears that these programmes could be threatened by public sector funding cuts.
Committee chairwoman Sandy Mewies urged the Assembly government to resist any cuts. "We consider that financial education has an even greater importance in the current economic climate: if individuals have less money coming in, they need to be smarter about how they utilise it," she said.
The committee heard calls for financial education to be given even greater status by becoming a GCSE subject, but stopped short of recommending this.
Rod McKee, ifs School of Finance head of financial capability, said: "Making financial education a stand-alone subject in the secondary school curriculum, equal in status to subjects such as history and geography, would go a long way toward addressing this problem."
The Welsh Financial Education Unit, set up by the Assembly government, is working on a two-year programme supporting teachers in primary and secondary schools. An independent evaluation of the unit is taking place and a report is due in 2011.
The Assembly government is looking at the Communities and Culture Committee report in detail and will respond in due course.
A spokeswoman said: "We have already taken steps to ensure that financial education is part of the revised curriculum, introduced in September 2008."
- Original headline: Children taught finance skills with `tainted' material sourced from banks