Science lessons in most Welsh schools are good but assessment isn't robust enough, according to school inspectors.
Estyn also says sometimes, in primary schools, teachers pass on their science misunderstandings to pupils.
The Welsh Government welcomes the report which it says is broadly positive.
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A grieving mother broke down in tears as she recalled how doctors could not find out what was wrong with her son in the run-up to his death.
Carol Morse claimed her 12-year-old son Ryan dropped to just four stone but doctors failed to act, Cardiff Crown Court hears.
Mark Prosser stabbed Billy Moore - a friend who had previously saved his life.