Pupils in England find science A-levels too difficult and other subjects more "funky", a House of Lords report says.
The government was accused of not keeping a pledge to improve labs
Physics especially suffered, the Lords science and technology committee said.
The problem was compounded by school league tables, "teaching to the test", poor labs, misplaced health and safety fears and a shortage of teachers.
The peers urged a broadening of the A-level curriculum, as in Wales. The government said it was already taking action to address many of the issues.
On Friday the prime minister stressed the importance he attached to science and urged youngsters to consider it as a career.
In its report, Science Teaching in Schools, the Lords committee noted a general decline in the popularity of science and mathematics A-levels over the last decade, though with an upturn in some subjects in the past couple of years.
One factor was simply fashion - with new options such as psychology, media studies and photography, which one witness to the committee said young people called "funky subjects".
For example, 50,000 students took psychology A-level in 2005, "significantly more than sat physics or chemistry".
A more serious and fundamental problem was that traditional science subjects and maths were regarded as more difficult.
Not only that, there was evidence they actually were harder, the peers said.
The response from the Department for Education and Skills and the Qualifications and Curriculum Authority, that all A-levels were given equal weight, was "unconvincing".
"The Institute of Physics reported anecdotal evidence of schools 'actively discouraging students from taking subjects that could weaken their league table position' through lower A-level grades."
The committee urged the government to revisit the recommendations of the Tomlinson Report, on having a range of diplomas to replace GCSEs and A-levels.
Its chairman, Lord Broers, said: "We call on the government to look again at a diploma or baccalaureate system, which would enable students to keep studying science and maths along with other subjects, reducing the tendency for them to drop science entirely for 'easier' subjects after their GCSEs.
"The Welsh Assembly Government has recognised the need to broaden post-16 education - the Westminster Government needs to catch up."
The report also expressed concern that the new "light touch" Ofsted inspections would mean there would be no future evidence base on the quality of science teaching in schools.
The stress on test results in schools prompted concern about "a culture of teaching to the test", pushing teachers into "narrow and uninspiring methods of teaching".
The committee deplored the government's failure to keep its 2005 election pledge to invest £200m in improving school science laboratories.
Even where facilities had been upgraded there was evidence that they were of low quality.
Witnesses had also reported "ill-informed" worries about health and safety in regard to science experiments and a "very real fear of litigation" if something went wrong.
Although the recruitment of teachers to shortage subjects had improved in recent years in response to government initiatives, the scale of vacancies in science and mathematics was "a major concern".
There also needed to be better ongoing training for science teachers, and a better career structure and rewards for lab technicians.
The Department for Education and Skills said increasing the number of scientists was a priority for the government, which was already making "significant progress" on delivering the actions being called for.
"We have been working across government with employers, schools and experts in the field to both improve the quality of science teaching and make science a more attractive option," a spokesman said.
"It is this joint working that will ensure we deliver the scientists of the future."