How do I turn a Yes/No field into a string?

I have successfully turned numbers and dates into strings that can get
concatenated with the rest of the code, but I cannot find Yes/No
examples. The part where I wrote [[[SOMETHING]]] is where I need to
enter something for Format that will turn Yes/No into a string.

'Turn Milestone Assessed into string (was number from 0 to 5)
Dim strMilAssessed As String
strMilAssessed = Format(Me.Milestone_assessed.Value(), "0")

'Turn Assessment Date into string (was date)
Dim strAssessDate As String
strAssessDate = Format(Me.Assessment_date.Value(), "MM/DD/YYYY")

'Turn Milestone Achieved into string (was Yes/No)
Dim strMilAchieved As String
strMilAchieved = Format(Me.Milestone_achieved_Value(),
[[[SOMETHING]]])

Thank you,
Rachel Garrett