A major row has erupted in schools over reforms which many teachers believe have "dumbed down" A-level maths, according to a report from the Government's exams watchdog.
The Qualifications and Curriculum Authority study said many 16-year-olds turned their back on maths because they believed the subject was "too difficult".
A level maths has become the preserve of "a clever core" in recent years but attempts to make the subject more "accessible" have split the teaching profession, the research found.
Some teachers were "shocked and appalled" by the changes to the A level, which came into force in September 2004. Others felt the new A levels helped all students to succeed.
The QCA reformed maths A level in 2003 in an attempt to make it more popular after exam entries slumped.
The changes meant sixth-formers could do four AS-level units and only two of the harder A2 modules and still get a full A level. Other subjects required three of each.
At the time of the reforms the QCA denied it was making the exam easier.
But the interim report from QCA researchers into the state of maths A level found large numbers of teachers disagreed.
"There is a split in the opinions of teaching staff about the role of A level mathematics and also in their reactions to the new specifications," it said.
"The split does not seem to be easily reconcilable. One group of teaching staff sees A level mathematics as being a subject where the maintenance of a high level of demand and wide scope of content are paramount."
This group views moves to make the qualification "more accessible" as "unacceptable 'dumbing down' of A level mathematics and something that makes it unattractive to their very able students".
"Other teachers see the reduction in content as a positive move in terms of helping all students to succeed, which they see as key."
The report stresses that cutting the subject content in the new maths A level was the most controversial issue.
The QCA's findings came in an interim report on participation in A level maths.
A spokeswoman for the QCA insisted that maths A level had not been dumbed down. She said: "The new specifications have yet to bed down. We will be continuing to look at it over the next 18 months. We do recognise that post-16 participation in mathematics is a cause for concern and we are looking to understand why that is and what we can do to improve this.
"But we will not do that by dumbing down mathematics."
The QCA insisted that the changes introduced in 2004 made the subject "more flexible" but not "easier".
* The QCA researchers conducted detailed work with 19 case study centres, launched a large-scale survey with responses from about 200 schools and colleges, and reviewed national data on A levels.