Watford boys' and girls' grammar schools and Parmiter's had their joint application for a judicial review turned down at the High Court on Monday.
They were objecting to a ruling in February by Andrew Collier, a schools adjudicator, to cut the number of pupils they select by ability by 10 per cent to 25 per cent for September's intake.
Watford boys' and girls' grammar schools are already considering putting the numbers selected by ability back to 35 per cent for September 2005.
They have already spent thousands of pounds on legal action.
Six months ago the two grammar schools won a judicial review against a similar ruling to cut numbers selected on ability. Martin Post, head of Watford boys, said Monday's decision could set a precedent whereby adjudicators could ignore the threat of repeated legal action by schools.
"It seems they can keep on hammering at our selection policy, despite a previous judgment, until they win in the end," he said.
Monday's decision was welcomed by Hertfordshire county council which had to delay the publication of details of secondary places for 16,000 pupils because of the dispute.
The OSA had the right to review the situation this year and, as well as looking at the two grammar schools, Mr Collier considered the intake at three other Hertfordshire selective schools - Parmiter's in Watford, Dame Alice Owen's, in Potters Bar, and Queens', in Bushey.
He ruled that both grammar schools and Parmiter's should reduce their selection, but said the other two schools had done enough to increase numbers of local children admitted.