Schools are in “chaos” after receiving “no guidance” from the government on which mock results can be used in place of official A-level and GCSE grades, heads have warned.

On the day before A-level results will be released, schools minister Nick Gibb said there was “no confusion” over the system for awarding this year’s grades, despite an “11th-hour” decision to allow mock results to be used in place of official estimates.

But teachers have taken to social media to raise “urgent” unanswered questions about how the process will work, including what counts as a mock, how grade boundaries will be standardised, and what happens if schools don’t have a central record of their results.

Related: ‘Unreliable’ mocks are open to cheats, teachers warn

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DfE: A levels and GCSEs will need appeals for mocks to count

And the Association of School and College Leaders has said that headteachers are in “chaos”, as they attempt to “field questions from parents and students without any information”.

A-level results: How will mock grades be used in appeals?

Maths teacher Steve Wren raised a series of questions for the Department for Education and exams regulator Ofqual on Twitter, including:

• What counts as a mock? Does it have to be a full past paper? A full suite of past papers? Some schools will do “cut and paste” of old papers to make up mocks as some topics will not have been covered. Others may write their own papers. Do these all count?
• Some schools may not have a central record of mock scores. They may reside in departments and people may be away on holiday, therefore presenting access issues. When do these need sorting?
• Students will have done mocks at different times, and some may not even have done one due to the shutdown. How will this difference be made fair for students?
• Some schools will use published grade boundaries, others will lower them to account for topics not yet covered. Are both of these allowed?
• Some students may have been absent for the mock but did the papers at home as homework a few weeks later when back at school. Does this count?
• Some schools did more than one mock. Can they pick the best?

Some urgent things for @educationgovuk (or @ofqual) to be working on. They probably have a matter of hours to sort these.

A) there is no national record of mock A level results. Basically any student could currently claim A* and nobody can check. These will need collecting.

- Yorkshire Steve (@Yorkshire_Steve) August 12, 2020

Geoff Barton, ASCL general secretary, told Tes that the announcement had left schools in “chaos”.

“The sudden announcement that mock results could be used by students if they are higher than calculated grades is bewildering,” he said.

“Mock exams are taken at different times, involve different papers, and some students won’t even have sat them.

“Teachers will have felt undermined by this decision, given that they have spent the last few months painstakingly assessing their students and providing centre-assessed grades to the exam boards.

“Obviously the concern is what happens when these centre-assessed grades are standardised by the exam boards, and it seems as though the 11th-hour idea of falling back on mock exam results is an attempt to head this off at the pass, even though it doesn’t make any sense.

“There is no guidance over how this will actually work, so our members are now left in a position where they will have to field questions from parents and students without any information. It is chaos.”