Ms Tattersall told a London conference on the future of assessment that what schools taught was driven by the content of exams. This trend had been growing since the advent of GCSE in 1988, and should be reversed.
She said: "We have testing at 11, 14, 16, 17 and 18. Students are going through the system hardly able to draw breath. The consequence is that the costs of examining have risen markedly.
"We need to redress the learning-assessment balance. We have to change the culture, from a dependency on an external end-of-course examination system to one in which assessment is varied, fit for purpose and takes place throughout the course. It also needs to be manageable and cost-effective."
Ms Tattersall said teacher assessment would have to be externally moderated if it was to be trusted. But she conceded that the public saw external exams as the only reliable indicator of pupils' progress. Teachers themselves, she suggested, needed to help change these perceptions.
Her calls, in a Royal Society of ArtsCampaign for Learning debate, will fuel the argument over assessment. The place of assessment, or coursework, within a possible English bac, is a key issue for the 14 to 19 taskforce which reports to ministers next year.
Meanwhile, Ken Boston, the exams watchdog, said this week his priority for this year's A-levels is to ensure that the "wheels don't fall off what is a virtually unsustainable process". This was an attack on the fact that millions of scripts will travel around the country by post under a system which also makes huge demands on examiners. Dr Boston wants to computerise the marking process, have more exams marked in dedicated centres and to reduce the number of exams.
He praised schools for putting teachers forward to mark papers after warning last autumn that last year's A-level regrading controversy could exacerbate the shortage of markers.
Although exam boards have not recruited all the examiners they need for this summer, more are in place than last year.
Dr Boston told a Learning and Skills Development Agency conference:
"Response from schools has been very encouraging."
* The Association of Colleges has called for traditional end-of-course exams to be replaced by assessment on completion of smaller units of work.