Extract from 'Primary school accountability 2018' - The floor standard is the minimum standard for pupil attainment and / or progress  that the government expects schools to meet.

School types and particular circumstances (floor standard)

As in previous years, there are some types of schools and particular circumstances in which floor standards do not apply.Floor standards do not apply to infant schools, special schools, independent schools, pupil referral units, alternative provision or hospital schools.
Schools are also excluded from the floor standards where:

•  there are fewer than 11 eligible pupils in their Year 6 cohort; or
• fewer than 50% of pupils have key stage 1 assessments that can be used to establish which prior attainment grouping the pupil should be allocated to.