"In both 2018 and in 2019, the first-year students who were more heavily incentivised by the fees reduction on average appear to have had a little bit of a more difficult time transitioning into university," she said.
"They were having greater difficulty in terms of their grade-point average. In terms of their perceived adjustment to university, confidence was lower.
"This doesn't necessarily mean that they weren't fully capable learners, but perhaps they weren't as prepared or perhaps they had different expectations about the workload and the different challenges associated with university study."
The students were also more likely to say they were thinking of dropping out of their courses, but the data had not yet been analysed to see if they followed through on that, Sotardi said.
The research indicated low achievement was linked to students' reasons for enrolling more than to their demographic backgrounds, she said.
"Instead of who students are in terms of their gender, their age, their ethnicity, the reasons why students pursue a university degree and whether they feel prepared seem to be more important when it comes to their academic outcomes and their experiences."
Potential students needed to be well-informed about university and know that even if there were no fees for their first year, there would be other costs, Sotardi said.
"There are lots of hidden costs like text books as well as in terms of their time and their energy."
Universities New Zealand director Chris Whelan said there was no sign the fees-free policy had led to big increases in enrolments or early drop-outs.
"Generally, if you're on a pathway towards university you've started preparing years before you get to university. Not many students get University Entrance by accident," he said.
"We're certainly not seeing anything like a larger number of students discontinuing and if we are it's more likely to be the impact of coronavirus at this stage."
Whelan said universities had good systems for identifying students who were struggling and helping them before they failed or dropped out.
Union of Students' Associations president Isabella Lenihan-Ikin said the research showed the policy was encouraging people who previously would not have considered tertiary study.
If students needed extra help, universities should provide it, Lenihan-Ikin said.
"When they're actually at the tertiary provider, whether it be wānanga, university or polytechnic, they should receive the support that enables them to continue studying, whether that be the academic support that helps them pass, whether that be the pastoral care or mental health support."
She said people should not measure the fees-free policy solely by its impact on enrolments.
"This is reducing student debt on an average of $5000-$6000 per student, which is enormous when you think about the individual benefit for that student."
A spokesperson for the Minister of Education, Chris Hipkins, said he had not yet received analysis of 2019 student enrolments.
However, the minister was confident universities would help any students who were struggling.
The spokesperson said since the introduction of the policy, borrowing for fees through student loans fell by $194 million between 2017 and 2018.
The minister had previously told RNZ that plans to make second and third years fees-free were not currently under consideration and the Government's focus was now on economic recovery after Covid-19.
- RNZ
