Flexslider startAt property – What’s required?

I have flexslider working in a WordPress website with custom navigation. However, I can’t get the startAt property to work. It always starts on the first slide. I’ve tried numerous modifications based on the Woo Flexslider page and what’s on github. No luck.

Here’s my javascript:

<script type="text/javascript" charset="utf-8">
  jQuery(window).load(function() {
  jQuery(".flexslider").flexslider({
  slideshow: false, 
  controlNav: true, 
  directionNav: true, 
  controlsContainer: ".slider-controls",
  manualControls: ".flex-control-nav li",
  startAt: 3'
  });
});
</script>

Have I missed something?