I follow a similar procedure to the one Pat suggested. Reading the sentences aloud really helps my students to know where the period or question mark should be.
I also retype passages from or summaries of our reading focus
story for the week to reinforce this skill. The passage is presented to students without capital letters, periods, or question marks. This seems to really help my lower students, because everyone is very familiar with the words and the meaning of the passage.
Initially, I put the passage on an overhead transparency and we read it aloud together and discuss where we think the sentence
end marks should go. After completing at least three or four different passages together, the students begin to try editing on their own.
This has been the most successful method for my students.