Scratch

You can let them be dragged by clicking the lock next to the Sprites name. Then, you can use this script

when  clicked
show
set 
sentence ▼
 to 
whatever you want the sentence to be
NO SPACES here
delete 
all  ▼
 of 
sentence ▼
forever
if 
mouse down?
 and 
touching color 
?
stamp
Insert 
whatever word this sprite is representing
 at 
last  ▼
 of 
sentence ▼

when 
space ▼
 key pressed
or whatever key you want
repeat 
length of 
sentences ▼
replace item 
1  ▼
 of 
sentences ▼
 with 
join
item 
1  ▼
 of 
sentences ▼
item 
2  ▼
 of 
sentences ▼
set 
person's answer ▼
 to 
item 
1  ▼
 of 
sentences ▼
if 
person's answer
=
sentence
say 
you got the sentence!
if 
not
person's answer
=
sentence
say 
you didn't get the sentence...

That would work where the first script would be under every sprite and the space key script would be on one sprite. It would only work if the people place the words in order of the sentence.