Scratch

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

when gf clicked
show
set [sentence v] to [whatever you want the sentence to be] //NO SPACES here
delete (all v) of [sentence v]
forever
if <<mouse down?> and <touching color [#EEEE00]?>>
stamp
Insert [whatever word this sprite is representing] at (last v) of [sentence v]
end

when [space v] key pressed //or whatever key you want
repeat <length of [sentences v]>
replace item (1 v) of [sentences v] with <join<item (1 v) of [sentences v]><item (2 v) of [sentences v]>>
end
set [person's answer v] to <item (1 v) of [sentences v]>
if <(person's answer)=(sentence)>
say [you got the sentence!]
end
if <not<(person's answer)=(sentence)>>
say [you didn't get the sentence...]
end

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.