Bonus points in Leaving Cert higher-level Maths have not necessarily improved standards in the subject.
Student uptake of the "honours" paper has doubled since the bonus of 25 CAO points for a minimum 40pc mark was introduced, but it has not been matched by a corresponding improvement in students' ability in maths.
Almost three in five teachers (58.5pc) do not believe that standards have improved, 22.6pc were unsure, while 18.9pc did see an improvement, according to research on the impact of the bonus points initiative.
In 2011, 47pc of higher-level candidates scored at least 70pc in the exams - but this was down to 37pc in 2018.
Many students moving up to higher level in the hope of getting the bonus are not putting in the effort to do well and are simply "hanging in" to get the minimum grade necessary, it found.
Meanwhile, teachers are struggling to adapt to bigger classes with pupils with a range of different motivations, with worries that higher attaining students are being neglected.
Some 266 maths teachers were surveyed for the study, and most reported that the bonus had a significant affect on the student profile in their classroom.
The most common change reported was that it resulted in people not suited to higher- level Maths persevering with it, to the detriment of some.
Almost all teachers (98pc) agreed that many students who were struggling at higher level were persisting because of bonus points.
As well as introducing a wider range of abilities to the "honours" class, teachers reported that it attracted less ambitious students aiming only to reach, rather than exceed, the minimum required, and students who were "not as hard-working" as the traditional candidate.
One teacher reported: "A lot of students now have the attitude 40pc will do."
The study adds: "As reported by teachers, current higher- level students are happy to study higher-level Mathematics without investing the time and effort required to improve their skills or excel."
The researchers conclude that while the bonus was successful in boosting participation at higher level, "it may not be having the desired effect" on attainment.
They call for more professional development of teachers focusing on the skills needed to teach and assess in mixed ability classes.
The findings are being outlined today at the biennial mathematics in education conference at Dublin City University by researchers Páraic Treacy of the University of Brighton, Mark Prendergast of University College Cork and Niamh O'Meara of EPISTEM, the national centre for excellence in science and maths education, based at the University of Limerick.
The research is due be published next week in the UK academic journal 'Research in Mathematics Education'.
Before the arrival of bonus points in 2012, typically 16pc of students sat the "honours" paper, while in 2018 it stood at 32pc.
The incentive aimed to acknowledge the perceived level of difficulty with the subject at higher level and also encourage greater uptake.