Lessons deemed fun are all well and good, but teachers must ensure that pupils learn from them.
Fun-filled busy classrooms can be deceptive - for they sometimes obscure the fact that children are not learning very much.
HMIE assistant chief inspector Alistair Marquis warned a gathering of primary headteachers that it was not enough for children to enjoy themselves at school.
"I want to see vibrant schools and youngsters learning in a fun environment, but it must not be at the expense of children's learning," Mr Marquis said.
He advised heads to be wary of "whims and wheezes that are not thought through".
Although he made no specific reference to A Curriculum for Excellence, it was a tacit warning that the advent of new and more flexible approaches to learning must not be at the expense of detailed planning. While heads have to be "prepared to take some risks", they should make sure that any innovations are "rigorously reviewed".
"Children only get one shot at this, so whatever else goes on, learning must continue at a high level," he said. "Pupils are let down badly if each day they can't answer `Yes' to two questions: `Have I learnt anything new today? And `Did I have fun today?'"
Mr Marquis, who was speaking at a conference in Edinburgh on leadership in primary schools, also told heads to get into classrooms on a regular basis. "If you're away from teachers and children, how do you know how to tell what needs to be done?" he asked. "To see the youngsters out of context is not helpful - it needs to be what happens in the classroom."
He also wants all heads to feel inspired about their jobs, and recalled a school he had been at where the headteacher said, "I hate children."
"If you don't have the passion for young people's learning and wellbeing, then you shouldn't be in the job," he said.
He warned, too, that a busy head was not always the sign of a successful school. It was easy to get "bogged down" in that business, leading to a situation where "somehow or other children don't seem to feature". Mr Marquis argued for casting aside the idea that leadership was about dominant, charismatic figures.
It should be about "leadership at all levels" and encouraging "reluctant leaders" who might be more shy about putting forward their ideas, but who could contribute "some amazing things".
"If you hold these people back, you're denying yourself access to that talent," he said.
He added that staff should constantly be encouraged to share ideas, rather than there being set times of the year where they could work collaboratively.
Parents, too, should be consulted about what is happening in the school: Mr Marquis still sees schools where parents feel "shut out" and the inspection process is the only chance for them to have their say.
Despite the tough-talking tone of much of his speech, Mr Marquis stressed that there was a lot to be happy about. Things had moved a long way since his schooldays, when headteachers would have "absolutely no focus on pedagogy" and acted more like "managers of bad boys".
"Overall, most get it right - and some outstandingly so," he said. "We can take pride in what's happening in our primary schools, by and large."