Jon Berry, convener of the anti-Sats alliance, said that members of his group had detected a "nervousness" among some teachers about what teaching would be like without the tests.
Last month, the National Union of Teachers backed down from a possible boycott of key stages 1 and 2 tests after less than a third of its members voted to take action.
Routine conversations with teachers had revealed their fears, said Mr Berry, a Hertfordshire secondary teacher. His alliance comprises mainly NUT activists.
He said: "We have found that there were a large number of teachers who were perhaps deterred from voting by the thought of what their working day would look like without what they saw as the direction provided by the tests.
"There was a widely stated dislike of the tests, but a nervousness of what it might mean on a day-to-day basis to replace them."
Mr Berry said that there were at least two groups in this situation. Some younger teachers had come through the system and were used to the testing regime. Others had already begun working towards this year's tests and were reluctant to see their work wasted.
The group is taking the finding as the spur for "re-invigorating" the campaign after what Mr Berry admitted was a setback. It is planning a conference in May in which academics will be invited to put forward a set of alternatives to tests in schools, drawing on international evidence.
The NUT's annual conference will discuss testing over Easter but Mr Berry said there needed to be a change of approach from "the same old formula", simply threatening industrial action.
The union has this month sent out a fresh survey to KS3 teachers, asking them whether they would support a boycott.
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