This probably isn't what you're looking for, but valuation of a company is always a very uncertain process. One approach is to add up the profits expected for the next 3-5 years, then use the final year's as an estimate of the longer-term out-years (flat) profits, use discounted cash-flow on those, and add the two pieces together to get the total value.
Again, tho', it's nowhere near being a science. Big companies use 50% of sales, but that probably wouldn't work for a small company, as you suggest.
50% of sales was a rough "rule of thumb" that I used as a starting point in this process. The problem is that old accounts receivable are included in the value -- and due to the nature of our work (for some of our projects the client retains 5% of the fee until the work is complete, which could be a long process) this number is quite substantial.
I suspect that the partners of this firm are operating under the misguided notion that an accurate method for assessing the value of this company is the same method that was used to assess the value of the (much larger) company where they both worked earlier in their careers.