Step 1:
This paper with plaid pattern on one side is 20x20 centimeters.
Prefold in half over both lines.

Step 8:
Make zig zag folds over the whole length, the mountain-folds are three squares apart.

Step 6:
Fold over this line, use the length of a doll as guidance.

Step 11:
Use tape or glue.

Step 10:
Prefold.

Step 9:
Tape / glue the upper part which goes around the waist.

Step 5:
Cut in half along the prefolded line and glue/tape both pieces together

Step 7:
Make zig zag folds over the prefolded lines.

Step 3:
Fold the edges to the centerline

Step 2:
Fold both halfs in three parts of the same size, see white bar as guidance.

Step 4:
Fold both edges to the centerline and unfold the model

Pictures: Girls walking around in the park, both wearing the same skirt, cool!

Done!
In this video Joost Langeveld shows you how to make the high school skirt: