My team and I have spent years establishing a world-class hiring process at Acceleration Partners (AP), but for all those efforts, I've found that one of the strongest predictors of success is still something right out of my grandmother's playbook: A thoughtful, well-written thank-you note.

Thank-you notes can tell you a lot about a job candidate. Here are the four qualities that stand out most to me.

Gratitude: People who show gratitude think about others and not just themselves--a valuable quality at any workplace. A 2011 University of Kentucky study found that people who are grateful have more sensitivity and empathy--attributes that tend to make people better leaders and team players.

Thoughtfulness: The best candidates don't send generic letters, they use the thank-you note to reflect on the opportunity and to describe how and why they are a good fit for the company. Such letters reveal candidates who are willing to spend extra time thinking about a task, which is a good sign they will invest effort in doing a good job.

Being Proactive: Writing a note shows that the candidate is doing what she can to get the job, not just waiting for the phone to ring. People who are proactive are often the best employees and the highest performers. Often, they also self-starters. These candidates are looking for opportunities to contribute and will put in the extra effort required.

Resourcefulness: Did the candidate have to dig up an e-mail address or a physical address to send you a thank-you note? If he did, give him a little extra credit. I often intentionally leave off contact info when communicating with potential hires, because I know that anyone who can't find my e-mail or address hasn't tried very hard. The best candidates do their research and don't make excuses. These are also the people who will also require less hand-holding on the job.

Here is an example of a letter I received that shows all of these qualities from an applicant to our company five years ago.

Hello Robert,

Thank you for your time to meet with me today. I enjoyed our conversation and I am excited about the opportunity with Acceleration Partners. I hope that you are as confident as I am that I will make a great addition to your team and be able to assist you in qualifying and retaining the right clientele. I am someone who works smart and works smart on the right things. I am creative and logical, and I thrive on a challenge and of course a little bit of chaos.

I could see today that you really enjoy what you do, and nothing would make me happier than being a part of your team. I promise you will not be disappointed in your decision. I look forward to speaking with you again.

This person started as an executive assistant and today runs our entire culture organization. She has been an incredible contributor to our team and to the company's growth.

Not all candidates write thank-you notes, and I'm not saying you shouldn't hire those who don't. What I am saying is that a great thank-you note is an excellent predictor of success. Personally, I can't imagine making a bid for a great job without writing one.

So, maybe Grandma was right.