GCSE exam success has dropped at two schools investigated in the Trojan Horse probe, the BBC understands.
Senior sources said just 58% of pupils at Park View School achieved five or more A* to Cs including maths and English compared with 75% last year.
At Golden Hillock it has fallen from 52% to 45%, they said.
The schools, which have not commented, were looked at amid claims some Muslims wanted to impose a more Islamic culture on the way they operate.
Birmingham MP Khalid Mahmood said the drop in results was the direct fault of governors and management of the schools, run by Park View Educational Trust.
"They were not working in the interest of the children that were there," he said.
"They were working in their own interest."
Investigations into the alleged Trojan Horse plot were sparked by the emergence in March of an anonymous letter purported to be a template showing how state schools could be taken over.
A number of schools were placed in special measures as a result of investigations by Ofsted.
Critics said the inquiries were distracting for pupils who were trying to focus on their GCSE exams.
Mohammed Ashraf, a Golden Hillock governor who quit alongside the rest of the school's governing body in the wake of the allegations, said his son's grades were short of those predicted.
He said his son was forecast Cs and Bs but achieved all Ds.
"The focus of the school's leadership and governance went to dealing with the issues of Trojan Horse and their attention should always have been on education," he said.
Correction 4 January 2017: This story has been amended to clarify that Mohammed Ashraf was not removed as a governor, but resigned alongside other governors.