The education select committee report on exam reform states that in 2011/12, 41.4% of pupils did not get five GCSEs, including English and maths, at grades A*-C.
It suggested the government should focus on improving the achievement of the "significant minority" that do not achieve five good GCSEs.
"While it is right to raise young people's expectations and aspirations, we fail to see how raising the bar will automatically result in more young people achieving higher standards," the report said.
"Furthermore, we have serious concerns about how well the proposed reforms will serve the 40% plus of pupils who do not achieve the Government's current floor standard."
More top news
Sarah Seawright's police photo was shared hundreds of times by fawning social media admirers after she was arrested for careless driving.
Zoo officials said the 17-year-old gorilla was killed to save the life of the boy who had crawled past a barrier into its enclosure.
Head of Germany's Protestant Church said 'extensive' Islam classes in schools could help prevent young Muslims from turning to extremism.