She said her school was worried that if easy and difficult papers were introduced a fifth of pupils would be entered for the wrong paper.
Ms Rogers was also concerned that boys, who traditionally do not do as well at GCSE as girls, would be entered for the easier papers, and this practice could lead to accusations of sex discrimination by parents.
Tiering, she said, forced teachers to divide pupils into "sheep and goats", a practice which was abolished with the end of CSE and O-levels and the introduction of GCSE.
Chris Woodhead, until recently chief executive of the School Curriculum and Assessment Authority, said teachers were divided over the issue of tiers, but when he appealed for a member of the audience to defend tiers no one did.
SCAA wants to introduce tiers to stretch brighter students, but critics say it has already introduced the starred A grade at GCSE for more able children, and in any case, the GCSE was already amply differentiating between bright and less able pupils.
Ms Rogers said after the conference that the problem with tiering was that teachers were too cautious. If they were unsure about which tier to enter a child for, they would choose the lower one because they would not want the pupil to fail.
There was nothing in the proposals about how pupils were to be compensated if teachers entered them for the wrong paper, she said.
Guest speaker at the conference, Eric Bolton, the former chief inspector of schools and professor for teacher education at the London Institute of Education, said that, although he favoured one common paper, there were disadvantages with both that and the tiering system.
In the end, he said, it came down to politics - the left favoured the common paper and the right favoured tiers.