In the markbook, the marks in the EYF column are linked to the EYF statutory assessment marks for subjects linked to this markbook.
In this example, we are looking at our current Year 1's. Note that Amy has a 2.0 under the EYF column.
The marks available to input for EYF statutory assessments are 1, 2 or 3. The reason some students have 1.5 or 2.5 is due to an average of the relevant EYF statutory assessment subjects related to this markbook ('Numbers' and 'Shape, space and measures' in this instance). You can check the students' assessment marks if you go to Admin > Students > Statutory Assessments and check these EYFS assessment components for the year the students took the tests.