Performing a particular series of movements, or positioning at precise coordinates, allows the player to jump onto walls 1.5 blocks in height (including fences, wall blocks, and blocks with slabs) without any effects or changes to attributes.

This is possible if the player would have been able to step up onto the block below the target block you're trying to get onto if the higher block were absent.

What I expected to happen was:
Player is unable to jump onto the 1.5 block high wall.

What actually happened was...:
Player jumps up onto the higher block, finishing 1.5 blocks up vertically from their initial position.

Steps to Reproduce (Method 1):

1. Create a 1.5 block high wall in front of you, such that if the block you are trying to get onto were omitted, you would be able to step up onto the lower block. For example, place a lower half-slab with another lower half slab of a different variety above it, as in the left half of the image.
2. Face directly forward and walk all the way until you are directly against the block and slab.
3. Tap the "s" key once to move backwards a small amount.
4. Turn 0.05 degrees to the left, or use a teleport command to do so.
5. Tap the "w" key once to move very close to the block and slab.
6. Jump by pressing forward one tick before hitting the spacebar.

Steps to Reproduce (Method 2):

1. Walk all the way against the wall/fence you are jumping onto.
2. Run the command "/minecraft:tp @s ~~ ~-0.00000001" (or the equivalent command for your facing direction).
3. Jump by pressing forward one tick before hitting the spacebar.