One of Wales' oldest Welsh-medium schools is urging parents to encourage their children to speak more of the language in the corridors.
Mr George wants pupils to revive their pride in the language
Arwel George, head of Ysgol Gyfun Penweddig in Aberystwyth, said Welsh had reached a "new low" outside the classroom.
He has appealed to parents, pupils and staff at the school to revive pride in their native tongue.
A language pressure group said Anglo-American culture was to blame.
Rhieni Tros Addysg Gymraeg (Rhag)/Parents for Welsh Medium Education, said English music and magazines played a major role in young people's lives.
In a letter to parents Mr George said: "During recent years there is a sense that there has been a decrease in the use of Welsh along the school's corridors.
"There has always been an element of this as Penweddig students are bilingual and using English, contrary to the school's expectations, is one means whereby young adolescents can express their individuality.
"By now, however, we feel that we have reached a new low and there is need for us as staff, students, parents and governors to realise what the situation is and pull together to revive our pride in the Welsh language and to strengthen its use in the life of the school."
Mr George added that he wanted to adopt a new slogan for the coming year: '2005: A successful new year for Welsh at Penweddig'.
Ysgol Penweddig opened in 1973.
Heini Griffith of Rhag said Welsh-speaking young people were under "enormous pressure" from the English language.
"English is the dominant language especially of youth culture. The Anglo/American culture dominates music and magazines and plays a large part in young people's lives," said Mr Griffith, who lives in Swansea.
Ysgol Penweddig is a Welsh medium comprehensive school
"Schools are left to deal with this and parents must take more responsibility to encourage their children to speak Welsh. Teachers take on too much responsibility for the language."
He added: "The problems at Penweddig are general problems seen in other parts of Wales and young people are under enormous pressure from English.
"I welcome Mr George's initiative and knowing him his message is positive."