So I have found a kluge of a work-around. Table Boxes, and their StringColBox() columns do allow justification. Below is a sample sccript that shows the concept.
names default to here(1);
dt=// Open Data Table: big class.jmp
// → Data Table( "big class" )
Open( "$SAMPLE_DATA/big class.jmp" );
// Create the Tabulate Table, and save it as a data table
(tab = dt << Tabulate(
Change Item Label( Statistics( Mean, "height" ) ),
Show Control Panel( 0 ),
Add Table(
Column Table( Statistics( Mean ), Analysis Columns( :height ) ),
Row Table( Grouping Columns( :age ) )
)
) )<< Make Into Data Table;
// Close the
thetable = current data table();
tab << close window;
// Only character fields can be justified, so change the 2 numeric columns to character
thetable:age << data type(character);
thetable:"height(height)"n << data type(character);
// Move the table to a journal, and close the table
thetable<<journal;
close(thetable, nosave);
// Center the fields
jr=current journal();
jr[StringColBox(1)]<<set justify("center");
jr[StringColBox(2)]<<set justify("center");
Jim