Education secretary John Swinney says he is 'wrestling' with the issues amid plans for a phased return to schools in August.
A charity has warned that delays in building an effective system in Scotland 'could cost lives'.
John Swinney told MSPs that coursework, existing grades and prior attainment will be used to assess grades.
Education secretary will set out the finer details of imminent school closures later.
Rural economy and tourism secretary Fergus Ewing is being investigated over claims from Marine Scotland staff.