The findings and recommendations of a controversial $300,000 review of special religious education and ethics classes in schools has been kept under wraps by the NSW government for up to nine months.

The review was a recommendation of a 2012 upper house inquiry into ethics classes in NSW schools, which found they should be retained as an option for students who do not want to take part in special religious education.

The inquiry recommended the Department of Education publish the number of students taking part in ethics (SEE) and special religious education (SRE) classes, or neither, and that both types of class be reviewed in 2014-15.

The review, by ARTD Consultants, cost $295,988. Submissions closed on July 31 last year and the review was due for delivery to the NSW government shortly after the contract period ended on December 31.