For Partner Check, pair students off and have them compare their answers to each other. When their answers don't match, they reconsider them to try to agree upon an answer. If they cannot agree, they need to be able to justify why they believe their answer is correct.
To respect the privacy of students, you may consider allowing them to pick their own partners. However, we all know how well buddies tend to work together...
Keeping the same partner for an extended length of time allows for completion accountability--the partner will be expecting the assignment to be done so they can participate together.
This Partner Check approach encourages students to really investigate whether their answer is correct or not, to defend their reasoning, and to be accountable to actually doing the assigned work so that their partner isn't let down.
For accountability, you can have students complete a form like this: