The consultant was employed by educational trust CfBT and discovered the test details from a colleague.
The not-for-profit trust suspended a number of staff members last April. It later took disciplinary action, but told The TES there was no security breach.
CfBT has a range of education divisions, including one inspecting schools on behalf of Ofsted and others providing school improvement services for Lincolnshire and East Sussex, which have 530 schools between them.
The consultant emailed a teacher prior to a revision session at the Lincolnshire secondary school in April last year, giving away a question that would be in that year's key stage 3 English Shakespeare paper.
In her email, the consultant wrote: "A colleague of mine is marking the reading paper. You haven't read this, but it seems the Shakespeare question is on character and motivation Macbeth's different reactions to the death of Duncan and of his wife. I don't know whether you'll be able to sneak this in ... !!"
The teacher reported the incident to her headteacher straight away who passed on the information to CfBT, via one of its inspectors, and her local authority.
The revision session was cancelled and the information was not used to help the pupils, so they were allowed to sit the exam.
A former staff member at the school, who provided The TES with a copy of the email, said: "For all I know this happened all over the county. The teacher came straight out with it and said 'This is cheating', but others might not report it."
CfBT employs 2,000 staff, has an annual turnover of pound;100 million and runs a handful of key government schemes, including the Young Gifted and Talented programme. It carries out projects in 40 countries from Kenya to Afghanistan, owns or manages six schools in the UK and is the joint sponsor of the St Mark's academy in Merton, London.
Richard Birkett, CfBT's commercial director, acknowledged the trust had been "alerted to an incident in connection with a revision training course for teaching staff due to be held at a school in Lincolnshire".
"Immediately CfBT informed the awarding body and the National Assessment Agency," he said. "It also suspended the staff involved.
"The awarding body and NAA investigated and were satisfied that no breach of security had taken place and decided to take no further action.
"CfBT then carried out its own disciplinary hearing and appropriate action was taken. It is not appropriate to comment on confidential employment issues relating to individual members of staff."
The Association of School and College Leaders says such incidents are rare.
But it is the latest in a series of cases where school staff could have been tempted to cheat because of the pressure to improve results.
A survey of 117 teachers by the Teacher Support Network last month found that two thirds admitted helping pupils more than they thought was appropriate to boost exam results.
The TES revealed this year how schools were spending hundreds of pounds to attend conferences given by senior examiners on how to beat the GCSE exam system.
Teachers were told to be "realistically generous" when marking coursework and give candidates in French a list of 42 questions and answers that might crop up in oral exams.