There are two options with this activity:
1) 3 students will hold the producers, consumers, and decomposer signs. Then, other students will be given a card which will require them to line up next to the student holding the appropriate sign. This could act as a review activity, or you could use it as a quick mini assessment.
For example- If a student gets the card that says koala they would stand behind the student holding the consumer sign.
2) You could have students work in groups of 2 or 3 and they can sort the cards. Students would use the producer, consumer, and decomposer pages as place-mats and they would place the organisms around them.
An answer sheet is attached. However, all of the organism cards are already categorized, so make sure you spread them out before the students see them. :)