"The side showed a lot of character and commitment especially in our defensive display to win last Friday's A game and that is pleasing because it reflects the spirit in the squad at the moment," said Lewis.
"It showed a clear improvement following our tour to South Africa in the summer. For example, when we were in front in the final minutes against England in August, our discipline let us down whereas on Friday our discipline and defence held up very well.
"In attack, we showed glimpses of the team's potential on Friday but we need to be more positive and creative if we are to score tries and win the full international.
"It's a huge experience for our players to come up against southern hemisphere sides and Australia in particular differ from many of the northern hemisphere sides we play against regularly. They look to play the game at a quick tempo and will always cause problems for our defence."
Lewis has developed a playing philosophy with Wales Under 18 which prioritises challenging the opposition with the ball in hand.
"International rugby at this level is not purely about winning games, it's about developing players for the future. If players are confident with the ball in hand at a young age, they will have more skills at their disposal as they move into senior rugby," he added.
"We don't have a large pool of players in Wales so we must maximise all the potential and raw talent available to us.
"Although we won on Friday, we have got to be more adventurous and play without fear of losing if we are to come out on top on Wednesday."
Wales Under 18 v Australian Schools
Wednesday 27 November, 7.15pm, The Gnoll (Tickets £3 adults, Under 16s £2)
Morgan Williams (RGC/ Llandrillo Coll/ Caernarfon); Rhys Geally (Ospreys / YG Gwyr / Pontarddulais), Garyn Smith (Blues/ Cardiff Met/ Pontypridd), Tyler Morgan (Dragons/ Caerleon/ Newport), Josh Adams (Scarlets/ Sir Gar/ Carm Ath); Luke Price (Ospreys/ Maesydderwen/ Abercrave), Tom Williams (Blues/ Treorchy Comp/ Pontypridd); Keegan Bale (Dragons/ Coleg Gwent/ Caerleon), Ryan Elias (Scarlets/ Sir Gar/ Carm Ath), Alex Jeffries (Dragons/ Coleg Gwent/ Newport), Joe Davies (Dragons/ Newport High/ Bedwas), Matthew Dodd (Ospreys/ Olchfa/ Dunvant), Jordan Viggers (Blues/ St David's / St Peter's), Ollie Griffiths (Dragons/ Newport), Jon Fox (capt, Ospreys/ Gower Coll/ Swansea).
Replacements: Liam Belcher (Blues/ Porth County / Pontypridd), Harrison Walsh (Ospreys/ Bishopgore / Mumbles), Leon Brown (Dragons/ Newport High), Seb Davies (Blues/ Coleg y Cymoedd / Pentyrch), Harri Keddie (Dragons/ Coleg Gwent / Caerleon), Dan Brooks (Ospreys/ Cardiff Uni/ Swansea), Dan Jones (Scarlets/ Sir Gar / Carm Quins), Joe Thomas (Ospreys/ Neath Port Talbot Coll / Morriston)
Australian Schools go on to play Ospreys Under 18 on Sunday (The Brewery Field, Bridgend 12.30pm) after the regional team won the right to play the touring side earlier in the season.