Official assessments of pupil performance in English Highers and Standard Grades this summer found some candidates had regurgitated prepared answers.
Principal assessors working for the Scottish Qualifications Authority (SQA) warned against using stock answers in future, saying they would result in lower marks.
Assessors went on to praise the work of pupils who had chosen to write imaginative essays in the Scots tongue, saying: "A number of candidates wrote with confidence, and effectively exploited the freshness and freedom this option offers them."
However, on the issue of teaching to the test, the SQA's 2013 report on Higher English creative writing said: "It was disappointing to see, once again, that in some centres, whole classes had been set identical tasks. In an exercise designed to encourage personal choice and individual interests, this is very unlikely to generate work of quality."
In an exam section on discursive writing, the SQA said a "limited range of topics" had been chosen, such as cosmetic surgery, abortion and euthanasia, adding: "There was a disappointing sameness about most of these essays and little sense of real engagement."
The report concluded: "There was evidence again this year of candidates coming to the exam with prepared answers, often on questions from past exam papers, and attempting to adapt these to fit the questions asked. Such answers lack relevance to the question and cannot access high marks.
"While class exercises are a worthwhile tactic in the teaching and learning process for writing, candidates should be allowed the freedom to choose the nature of their final submissions."
The SQA's report on Standard Grade also warned against pre-prepared answers. There were also concerns over some candidates "lifting" sections of text directly from websites.
On the issues of technical accuracy, it raised concerns over punctuation, misuse of capitals, inaccurate paragraphing, spelling errors and uncertainty when punctuating direct speech.
The report says teachers should urge candidates to use internet sources carefully and to focus on technical accuracy.
Alan McKenzie, acting general secretary of the Scottish Secondary Teachers' Association, said the approach of drilling pupils in set answers was understandable given the pressure on teachers to get candidates through exams.
"When you are preparing pupils you have to create a structure for the exam work and in doing so you create a sameness that could be criticised," he said.
"In some subjects, where large numbers of pupils of all abilities are being taught in one class, teachers will inevitably spend more time on that structure rather than working to stretch the better candidates.
"That approach will not get best marks for them, but it will get a lot of marginal pupils through the exams, which is good for them."
Iain Ellis, chairman of the National Parents Forum Scotland, said: "We are confident schools will pay close attention to the SQA's comments and hope the SQA has made this information available directly to schools.
"The new Curriculum For Excellence creates many opportunities for personalisation and choice for children and young people. It is more important than ever schools support this so pupils are confident in making their own choices in their qualifications years.
"We look forward to the SQA not having to make a similar statement when the new Highers are introduced in 2015."