Children's understanding and mastery of topics covered will primarily be assessed informally. Observational assessments and anecdotal records can be kept where appropriate. Since each new activity and topic introduced will be building on the prior activities and topics, assessments will naturally to be ongoing.
As students move into some of the more independent sections of the unit, you could incorporate some individual literacy based assessments. Review each student's journal individually with them. Ask them to recall and discuss their entries. Check for such skills as: letter recognition, site words, fluency in reading, connecting words to pictures, 1:1 correspondence, number recognition, ordering sets, connecting sets to numerals, fractions and counting. Journals are one way of really keeping running records of student's work in order to assess their skills over the course of the unit.