In a large highball glass (16 oz), muddle together the simple syrup, sliced strawberries and mint leaves. (Muddling is a technique used to gently mash herbs and/or fruit to release the essence or juices. I recommend using a muddler for best results, however the back of a wooden spoon can be used in a pinch.)
Stir in the rum and lime juice.
Top with ice (to the top of the glass) and then top with club soda.
Garnish with mint and strawberries, if desired.