A $2 million federal grant to a trades training school associated with former Family First senator Bob Day is under investigation by the Auditor-General.

The Australian National Audit Office confirmed on Monday it would investigate the effectiveness of the $1.84 million grant to North East Vocational College, in suburban Adelaide, after Mr Day lobbied a string of ministers for the cash to fund his pet project "student builders".

A report due in April will consider if the Education and Training Department established the program in accordance with federal government grants rules and guidelines.

Shadow attorney-general Mark Dreyfus sought an investigation into the grant last year, coming as the High Court considers Mr Day's eligibility to stand for the Senate over an apparent financial interest in the building that housed his Adelaide electorate office.