Archway secondary school in Stroud offers courses for parents in maths, literacy, design technology and information-gathering.
Gill Buckeridge, who runs the Archway project with Jane Palmer, of Stroud College's adult basic literacy team, said: "At primary schools, parents often go in to help with reading, but at secondary schools that contact is often lost.
"We were finding that schools had changed so much that parents didn't understand the work their children were being asked to do. They wouldn't have any idea how to help their child do a design brief for design technology, " she said.
Another problem was that parents who had taken exam-based O-levels and CSEs found it hard to understand the proportion of coursework involved in GCSEs. "That meant some pupils were able to 'swing the lead' - telling parents that writing a couple of lines was enough, when what was involved was a major assignment that should have been almost a term's work," she said.
One father, Richard Powell, 45, joined a maths course after finding he could not help his dyslexic son, Luke, with homework. "The way maths is taught is so different from what it was in my day.
"Luke is not thick, but he is slow and he has never had any confidence. I thought it would help him if I went with him to show I was willing to learn, " he said, adding that Luke's maths was now much improved.
Each course is taught by a subject teacher alongside a specialist in adult basic education, at a cost of about Pounds 400.
Initial cash came from a European Social Funding grant, which has now ended, and some Further Education Funding Council money has now been obtained for maths and English.