David Burke, Presbyterian teacher of theology from Sydney writes a brief article about the frequency of celebration of the Lord’s Supper.
I’ve recently been thinking that, in contrast to an understanding of gathered worship that emphasises it as being a witness to unbelievers, the celebration of the Lord’s Supper as a means of grace demonstrates that gathered worship is primarily for God’s people to receive His grace, the secondary effect of which is witness to those who are not part of His kingdom.
Though that is not entirely an adequate way of phrasing it either.
I would think that Presbyterians believe that covenant children may be partakers of the grace conferred through the supper, though they are not partakers of the physical elements.
The article begins:
I was recently part of a church that celebrated the Lord’s Supper weekly – a simple act within the regular Sunday service. At around the same time I visited a Christian college that celebrated the Supper twice within four days (once at a commencement service and another at a college retreat). I have been a pastor in churches that did so quarterly and another did so monthly.
All this prompts me to ask: how often should the Lord’s Supper (or Communion or Eucharist) be celebrated?
Christian practice varies from daily celebration, weekly, monthly, quarterly, annually, spasmodically or never…
mgpcpastor's blog 
Quarterly seems, to me seems to be too far apart and we need to remember what Christ has done for us more often, weekly seems too often and becomes habitual, often without serious thought of what we are doing. I know this is personal and we should pay diligent attention to worship and the sacraments whenever they are brought before us. Monthly, seems to me, to be a good balance for each of our services, those who attend both, of course, celebrate fortnightly.