For every puzzle put a dot in each square in the left column and dot in each square where a ball exits the grid. If a ball exits the top row, that row must also be filled with dots.

Then take careful note of how many blocks are to be used. If it is a low number, look for a simple solution where some of the balls roll straight across. If it is high number, look for ways to cram extra blocks into areas that will never see a ball. Next determine where the ball on the bottom row will exit the grid.

Here are the answers we came up with. The blank squares indicate places where blocks could optionally be placed if we needed to use more blocks:

Puzzle 1, Place 3 blocks.

Puzzle 2, Place 3 blocks.

Puzzle 3, Place 6 blocks.

Puzzle 4, Place 13 blocks.

Puzzle 5, Place 5 blocks.

Puzzle 6, Place 15 blocks.