The parents have campaigned for five years to overturn Dyfed County Council's bilingual education policy, under which English-speaking children in predominantly Welsh-speaking areas must attend Welsh language schools. Pupils there are not taught in English until they are seven, after which they have lessons in the subject.
Six thousand of Dyfed's 33,000 schoolchildren attend schools at which they are not taught in their mother tongue. While some parents are happy with the rules, others say they mirror the old system under which Welsh pupils were forbidden to speak their native tongue.
John Latter, spokesman for the group, known as Education First, said it would take its case to the European Court of Human Rights if it fails in the House of Lords. Last week, the Court of Appeal rejected the parents' claim that Dyfed's policy was illegal.
All children should be able to learn in their first language when they started school, Mr Latter said. There should be bilingual schools instead of the existing single-language ones, or, failing that, children should have free transport to the nearest school which teaches in their first language. 'Most Welsh-speaking children live in the areas where the Welsh medium schools are, but there are cases where parents would prefer their children to be educated through Welsh and the facility isn't there. I would support their case too.'
Jill Sherwood, one of the campaigners, does an 18-mile round trip from her home in Llangolman to take three of her 10 children to an English primary school in Narberth. She says she was happy to accept the new policy when it was introduced at her local school six years ago, until she realised that teachers were refusing to speak English to her son, Dominic, then aged four.
Dyfed has denied that teachers speak Welsh to children even when they cannot understand it, and maintains that its policy is a flexible one.
John Thomas, chairman of the education committee, was 'delighted and satisfied with the outcome of the judgment but we regret this matter had to go to such lengths and expense to justify Dyfed's legal application of the policy'.