Board Thread:LOC General Discussion/@comment-142.177.220.17-20130310171958/@comment-5933544-20130310172631

The skill effect stays the same, but the potential of that skill reaches maximum at lv10.

For example, Atum of Vitality has a Med-boost to Water ATK. At lv1, its skill, Life Absorption will provide 10% boost to Water ATK. As its skill level increases, the effect of that same skill grows more influential, to a maximum of 20% at lv10.

To sum it up, Small boots don't turn into medium, large or great as its lvl increases, but acquires a better effect.

For more information: Skills.