Training children in mindfulness may help to improve their ability to tune out distractions and allow them to focus better according to a study presented at the British Psychological Society's Cognitive Developmental Psychology Annual Conference.
Inattention and Focus Difficulties
One of the three major symptoms of ADHD is inattention. Some experts believe a better way to explain this would be "over" attention, or paying attention to every detail in a situation. For example, the child sitting in a classroom has a hard time focusing and paying attention to the teacher because he is paying attention to the ant walking across the floor, the boy several rows over playing with a pencil, the birds singing outside, the noise in the hallway. In other words, it is not that he isn't paying attention, it is that he is unable to filter stimulus in order to focus on one particular thing.
What is Mindfulness?
Mindfulness is being fully present in the moment. It is being fully focused and aware of what is happening right now. It is being aware purposely. The website WildMind.org gives an example of eating:
"When we are purposefully aware of eating, we are consciously being aware of the process of eating. We're deliberately noticing the sensations and our responses to those sensations. We're noticing the mind wandering, and when it does wander we purposefully bring our attention back.
When we're eating unmindfully we may in theory be aware of what we're doing, but we're probably thinking about a hundred and one other things at the same time, and we may also be watching TV, talking, or reading or even all three So a very small part of our awareness is absorbed with eating, and we may be only barely aware of the physical sensations and even less aware of our thoughts and emotions." 
An important aspect of mindfulness being aware without judgment. You should notice your thoughts, be aware of your thoughts, but not judge them as negative or positive, rather, they are just thoughts. You accept the thought and then let it go.
Monks and high priests have practiced mindfulness meditation for centuries, but it only recently became popular in the general population. Research has shown practicing mindfulness on a regular basis lessens anxiety and depression and increases feelings of well-being.
Mindfulness and ADHD
In the recent study, 30 children between the ages of 10 and 11 years old took a mindfulness course as part of their school curriculum. Researchers measured levels of mindfulness with a questionnaire and measured attention skills via a computer game designed to measure attention. Measurements of both mindfulness and attention were taken at the start of the study and in three-month increments during the study.
The results of the study showed an improvement in ability to focus and deal with distractions. Dominic Crehan, one of the authors of the study stated, "The ability to pay attention in class is crucial for success at school. Mindfulness appears to have an effect after only a short training course, which the children thoroughly enjoyed! Through their training, the children actually learn to watch their minds working and learn to control their attention. These findings could be particularly important for helping children with attention difficulties such as ADHD. Further research on the effects of mindfulness on children's attention is very much needed." 
 "Mindfulness Training Improves Attention in Children,"2013, Sept 3, Staff Writer, British Psychological Society
 "What Is Mindfulness?" Date Unknown, Staff Writer, WindMind.org