The focus on developing literacy and numeracy skills in primary schools is contributing to a decline in the standard of science lessons, according to an expert body.
The Association for Science Education (ASE) said high-quality continuing professional development must be prioritised to boost primary teachers' confidence in teaching science.
It comes after a cross-party group of Assembly Members voiced "deep concern" over the falling standards of primary science in a major report into the STEM (science, technology, engineering and maths) agenda.
The Enterprise and Learning Committee's report said that although there was a "mixed picture" in primary schools, there had been a recent decline in standards in science and maths relative to other subjects. It has urged the Assembly government to investigate.
Marianne Cutler, a director at the ASE, said: "In primary schools the emphasis on literacy and numeracy is taking up more time for teachers. They have had less time to develop science than they have in the past.
"When they have to teach certain things in science that are perceived as difficult, some primary teachers, especially those without a science background, find it difficult and feel they need more support to bring it to life.
"You can do a lot with very exciting initiatives like taking children outside the classroom and bringing experts in, but if the experience as a norm is not as good as it should be, those additional support mechanisms won't count for much."
Ms Cutler said good CPD will have long-term benefits and help pupils engage with the subject.
The committee also heard evidence from Welsh inspectorate Estyn that suggested a lack of scientific capacity in local authorities and that advisory services could be partly to blame for the decline in standards.
There is also a shortage of science specialists in the primary school workforce and the subject is no longer a core part of the assessment framework in some schools.
The report said: "Whatever the causes, this trend deeply concerns us. Positive experience and engagement with STEM at primary level is key to pupils being enthused to continue with those subjects in their later education and careers."
It recommended the government publish a continuing professional development plan for teachers aimed at improving in-service training and updating for STEM teachers and heads of department to enhance their subject knowledge and understanding of how to teach specific subject topics up to GCSE level.
It said the government should encourage more schools to offer triple science and conduct research into the relationship between pupils' study of science at GCSE and their final A-level grades.
A spokesman for the Assembly government said it would take time to consider the report and its 22 recommendations.
He added: "The minister has made a clear commitment to raising standards across the board in Wales. We are actively encouraging the take-up of STEM."
APPLIANCE OF SCIENCE: Hook them and stretch them
Primary teacher Linda Curwen, who recently won a prestigious award for "refreshing and enlivening" science at St Fagan's Church in Wales Primary, Cardiff, said that lessons need to grab pupils' attention.
At St Fagans, science is taught as part of a themed curriculum, and Ms Curwen has been invited to share her innovative skills-led and enquiry- based approach with colleagues from other schools.
"We're always trying to find something to get pupils hooked on the subject. We start with a big, engaging introduction, explore what they know and then set them a challenge to take it further.
"We try to find meaningful ways of connecting it to other subjects so they can see links to other aspects of the curriculum."
- Original headline: Focus on numeracy and literacy `leaves science in decline'