Mr. Zellman's class - Something's Missing
by Ron Sweet

Six of the answers become new, shorter words before entry in the grid.  The   
unclued entry at 11 Across gives a hint as to what happens to these six words.
To disguise which words get changed, all answer lengths have been omitted.  

Across 1 A mob rolls crazily in dance halls 7 Significant years are making a comeback 9 Grooves in the road rust badly 10 Della returned after child added numbers together 11 See instructions 12 Scold members of Chamber at eleven 16 Tilt like meat with very little fat 17 Individual running home, finally 18 Hal enters, not as fast and not as deep

Down 1 Incorrectly label beginning of tap dance 2 Starts to order all the grain used in Cheerios 3 Oregon is confused about a spice 4 Leaders of motocross usually drive in wet dirt 5 Young man at end of line embraces tall action hero Sylvester 6 Terrain surrounded by water is empty landscape 8 Actor's part in “Dinner Bread,” we hear 11 Having the skill to manipulate bale 13 Cheer every other breath 14 Fat used in candles initially takes permit 15 That girl's hero, almost

Solution