I love incorporating natural elements into student work.
To make things easier, I divided a tray in half with masking tape. They scooped some acorns and emptied it onto one side of the tray. The kids moved the acorns from one side to another and tallied them on a recording sheet as they went. After making a bundle of 5 tally marks, they could count to five again. I find that if they try to tally while counting over 5, it gets all mixed up.
Once finished, they counted their tally marks and could check their work by counting the acorns. Then, they chose a different scoop and did it again. One tip, don't use measuring cups more than 1/3 cup or it will take forever to tally. Who knew more than 50 acorns could fit into 1 cup?!