In a large mixing bowl, beat the softened butter and granulated sugar until light and fluffy. Mix in the egg and vanilla extract until fully combined.

In a separate bowl, whisk together the flour, baking powder, and salt.

Gradually add the dry ingredients to the butter mixture, mixing just until a soft dough forms.

Divide the dough into two discs, wrap well, and refrigerate for at least 30 minutes.

Preheat the oven to 350°F and line baking sheets with parchment paper.

On a lightly floured surface, roll the dough to about 1/4-inch thickness. Cut into school-themed shapes and transfer to the prepared baking sheets.

Bake for 8 to 10 minutes, or until the edges are just set and the tops look dry.

Let the cookies rest on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before decorating.

In a clean bowl, beat the powdered sugar, meringue powder, warm water, and vanilla extract until smooth and glossy. Adjust with additional water as needed for piping and flood consistencies.

Divide the icing into small bowls and tint with gel food coloring, keeping one portion white.

Transfer icing to piping bags or squeeze bottles and pipe outlines on each cookie to match the design.

Fill in each outlined section with slightly thinned icing. Use a toothpick or scribe tool to guide icing into corners and pop air bubbles. Add details like notebook lines, ruler marks, pencil tips, and bus windows once the base icing begins to set.

Leave the cookies at room temperature until the icing is fully dry and set before stacking or packaging.