Check Box on a SubForm

I have a table (Table1T). It contains 2 fields, ID and CheckBox. The CheckBox is Yes/No and the default as NO (ie No check). I have a subForm (SubFormF). The subForm is bound to the Table1T, The subForm has a CheckBox. It gets its data from Table1T. When the CheckBox on the subFom is checked, the CheckBox field on the table Table1T should show a check. It does not. Any ideas as to why not? Thanks.