They have won a ruling from the Schools Adjudicator preventing Tory-controlled Kent council from delaying secondary admissions until the 11-plus results are known.
The Stop the Eleven Plus campaign (STEP) argued that this would, in effect, allow parents of pupils who failed the test two chances to choose a school and that children not entered for the 11-plus could lose places at popular schools as a result.
Their view was backed by the adjudicator who found that the proposed arrangements would be unfair to those not taking the 11-plus.
He said that a delay in admissions arrangements was "in the interests of a minority of parents" at a time when most "will be anxious to know what school their child will attend".
But he backed Kent's attempts to standardise admissions procedures in the county. Parents will now be asked to register their preferred school in November rather than February.
Martin Frey, spokesperson for STEP, said he was delighted with the decision. "I think this will reduce the number of pupils taking the 11-plus," he said.