Last month, National University of Singapore economics lecturer Kelvin Seah analysed survey data from the Programme for International Student Assessment (Pisa) in 2012 and made a surprising finding: Students who had tuition fared worse than those who did not.
Dr Seah, 34, said he came to two conclusions: "Either these students were receiving tuition because they were weaker in the first place or they did worse because of tuition. That means tuition and having too many lessons might be counter-productive."
Education experts said it is difficult to establish how much of a role tuition has in academic success or if it has contributed to Singapore's stellar showing in Pisa, a global benchmarking test which 15-year-olds here topped last year.
But what is beyond dispute is the growth of the shadow education industry. Tuition is worth more than a billion dollars annually here, almost double the $650 million spent on it in 2004.
Some parents spend several hundreds or thousands of dollars on tuition each month, despite knowing that having tuition may not raise their children's grades significantly.
This stems from a strong commitment to education in Singaporean families - doing well at national examinations is a priority for many parents and students.
Dr Yeap Ban Har, 48, principal of Marshall Cavendish Institute, which conducts professional development courses for teachers, reckoned tutoring helps in mastering the basics, but does not contribute significantly to performing well in novel, challenging problems.
"If a student is weak in basics, tuition might help with basic skills questions as it tends to be about practice and more practice," he said. "But it may not help with challenging, novel ones, like those found in the Pisa exercise."
National Institute of Education don Jason Tan said the efficacy of tuition varies from student to student. "I don't think you can say tuition does not work for anyone."
Experts said tuition will exist as long as there are high-stakes national examinations.
Dr Seah said tuition should not be lightly dismissed. "For students whose families can afford better-quality tuition and enrichment, it could be a big part of why they continue to do well."
Dr Yeap said the skills of a teacher make more of a difference in a student's learning process. "It is not a case of tuition or no tuition... If a teacher can create opportunities (for students) to explore, to collaborate, to think structurally, to reflect, to communicate, to be independent, to make meaning, to be confident… It does not matter whether he is a teacher in a school, or a tutor."