Minecraft wiki entry for Hardened_Glass_Pane, associated text: "Hardened Light Blue Stained Glass Pane" and "Hardened Light Gray Stained Glass Pane" each hold the record for the longest name of any block in any version of Minecraft, both at 33 characters excluding spaces (38 including spaces).
The record holders outside of the Education Edition are the "Cracked Polished Blackstone Bricks" and "Polished Blackstone Pressure Plate", both at 31 characters excluding spaces (34 including spaces).