Lizzie listened to the professor and then looked at her wand, thoughtfully. Sustaining the shield.. hmm. She knew she had the spell and the movement of the wand, so according to her checklist it must be the focus that wasn't strong enough. With a sigh she kept trying, now trying her hardest to cut out the surroundings like she did when she read. It worked quite well, the shield stayed longer each time. She was definately getting better at this by every try. Happily she continued, too focused to hear the surroundings. Protego!